Category Archives: Information

CodeCard, Information, REST

CodeCard Sketch changes: Howto disable fingerprint check and increase REST URI size

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Pre-Requisites

  • You have followed the instructions here.
  • You are comfortable using the Arduino IDE and making changes to the Sketch.

Fingerprint Check

In the comments on the post You Went to Oracle Open World 19 and got a Code Card, now what? we talked about how to update the fingerprint of the security certificate for the REST API when it changes.

I’m not a big fan of doing things multiple times and since I’m not planning on doing anything of a sensitive nature with my CodeCard I decided I would just disable the fingerprint check altogether.

How to tell if the fingerprint check is causing your badge to stop working.

If you push one of the buttons and it hangs on the “Please wait…” screen forever, check the Serial Monitor for a message similar to this.

Warning, If you’re planning to use your CodeCard for anything you’d consider sensitive, do not make this change!

Upgrade the driver

  1. Clone or download the CodeCard repository
  2. In the Arduino IDE, open the file codecard/arduino/codecard/codecard.ino
  3. Open the Board Manager.  Tools/Board/Boards Manager
  4. Search for esp
  5. Select version 2.5.2
  6. Click Install
  7. Close the Boards Manager
Code Changes
  • Click on the httpClient.h tab
  • Replace line 74 with BearSSL::WiFiClientSecure client;

  • On line 102 add client.setInsecure();

  • Comment out the fingerprint check starting on line 112

  • Uncomment line 152 and remove line 153

  • On line 176 add secureClient.setInsecure();

  • Comment out the fingerprint check starting on line 185

Increase arrayToStore variable size

If you’re planning to change the REST calls to use a different and longer URI you will want to increase the size of the arrayToStore variables.  Currently they are set to 100, I changed mine to 200, but you can use whatever you’d like.

  • Click on the memory.h tab
  • On lines 18 and 46, change the arrayToStore variable to the new size
  • Click on the wifi.h tab
  • On line 7, change the arrayToStore variable to the new size

Troubleshooting

Sketch uses too much program storage space

I have seen this error off and on when I compile the sketch.  If you get this error, the easiest way to reduce the size of the sketch is to remove some of the larger icons in icons.h.

  • Click on icons.h
  • Find a 128x128px image that you don’t plan to use and either comment it or remove it.
  • Click on templates.h
  • Find the drawIcon128(int x, int y, String icon, long color) method and comment or remove the reference to the image you removed.
  • You may have to remove more than one image.
“Connection failed” or you receive an empty response “{}”

This one can be tricky.  The way I’ve solved this is to erase the ESP8266 flash memory.

Usually this works:

  • Connect with the Serial Monitor
  • Press and release the A and B buttons
  • Wait for the Serial Monitor to display all of the data
  • Enter “reset” and send
  • Enter “ls” and update any settings as needed

If that doesn’t work you may need to search for another way to reset the memory.  Please leave a comment if you have a better way.

 

CodeCard, Information, Python, Tools

You Went to Oracle Open World 19 and got a Code Card, now what?

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We handed out several hundred Code Cards this year and I’m guessing a few of you are wondering what to do next.

If you got home and pressed one of the buttons you more than likely saw this screen.

Don’t worry, it’s not broken, you just need to get it connected to the internet.  There are a few different ways to do this.

Note: The Code Card uses a 2.4 GHz WiFi connection.

Create a WiFi Network

The easiest way to get it connected is to create a WiFi network using the credentials that are already set on the Code Card.

One way you can do this is to create guest network on your WiFi router.  Please refer to your router manual for instructions on setting this up.

Alternatively, you could create a hotspot on your phone, but make sure you’re OK with any charges from your service provider.

Edit:

At Oracle we like to keep everything patched and up to date.  After I published this post, the security certificate for the REST back end was updated.  This means you will also need to update the fingerprint settings for the four button options.

This also means that creating a WiFi SSID as in the paragraph above will only work if you also update the following four settings.  For that you’ll need to choose one of the methods below.   (I have added them to the examples below.)

Change the WiFi credentials on the card

If you’d rather just connect the Code Card to your existing WiFi network (2.4 GHz only), you can change the settings on the card.

In order to do this you need to open a serial connection to the card and send the following commands (using your WiFi credentials):

A Little Python

If you’d like to use Python:

  1. Install Python 3 if you don’t already have it.
  2. Open a terminal and install pyserial.
  3. Create a file using the following code.  I named mine ccSerial.py.
  4. Change lines 7 and 8 to use your WiFi credentials.
  5. In the terminal run the new module and follow the instructions.
    You should see something similar to the following.
Arduino IDE

If you have a Serial communication tool that you like, you should be able to use it to change the settings.

If not the Arduino IDE includes a Serial Monitor tool that work great.

  1. Do not connect your Code Card to the computer yet.
  2. Download, install and run the Arduino IDE.
  3. Click on Tools / Port.
  4. See what Ports are already in use.
  5. Connect your Code Card and turn it on.
  6. Click on Tools / Port.
  7. The newest Port should be your Code Card; select it.
  8. Click on Tools / Serial Monitor.
  9. On the bottom of the Serial Monitor, choose 115200 baud.
  10. Turn your Code Card off and on again.
  11. Press and release the A and B buttons at the same time.
    You should see something like this.
  12. In the input field at the top enter (use your SSID)
    Click Send.
    You should see something like
  13. At the top enter (use your password)
    Click Send.
    You should see something like
  14. At the top enter (use your password)
    Click Send.
    You should see something like
  15. At the top enter (use your password)
    Click Send.
    You should see something like
  16. At the top enter (use your password)
    Click Send.
    You should see something like
  17. At the top enter (use your password)
    Click Send.
    You should see something like
  18. Unplug your Code Card.
  19. Turn it off and on again.
  20. It should now connect to your network and the buttons should work.

What Else Can You Do?

There are a lot of things you can do with your Code Card.

For some ideas check out this GitHub page for some how to guides and other information.

Information, Learning, REST

How to secure your ORDS service

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Securing your Oracle Rest Data Services module only takes a couple of minutes.

As you can see in the video, this will be a fairly short how-to.

Assumptions

For this post, I’m going to assume:

  • You’re able to use SQL Developer.
  • You already have an ORDS module created that you want to secure.
  • You have at least a basic understanding of Roles, Privileges, Authentication and Authorization.

Test the Existing Service

Before we begin, I’ll test the current service with a curl command.

This returns a response with a status of “HTTP/1.1 200 OK” and a JSON object with an array of items.

 

Secure Your Service

First up I will create a Role and a Privilege that I’ll use to secure my service.

Create a Role
  1. Expand the schema connection and REST Data Services, if they are not already expanded.
  2. Right click on Roles.
  3. Click New Role…

  1. Enter a name for the role.  I’m using bc-role.
  2. Click Apply.

Create a Privilege
  1. Expand the schema connection and REST Data Services, if they are not already expanded.
  2. Right click on Privileges.
  3. Click New Privilege…

  1. Enter a name for the privilege.  I’m using bc-priv.
  2. Select the new role ‘bc-role’.
  3. Select the ORDS Module.  I’m using my Beacon module.
  4. Click Apply.

Be aware, this will only add security to the specific modules you select in the bottom section.  If you were to add a new module later and you want it to be covered with this privilege, you need to remember to edit this privilege and select it in the ‘Protect Modules’ selector.

Alternatively, you can use the ‘Protect Resources’ tab to apply security based on a URI pattern.

For my examples, I’m working from a VirtualBox VM and I have used ‘beacon’ as my schema alias.  So the base for all of my REST services in this schema would be

I entered the URI pattern

This will protect all ORDS services for this schema.  If I wanted to use this method to protect just an admin URI template in my beacon module (the full URI is https://localhost:8080/ords/beacon/beacon/admin), I would use a URI pattern like this

There are many more complex patterns you could use for your services, but for this post, I am only protecting the Beacon module so I am using the first example.

Test
This now returns a response with a status of “HTTP/1.1 401 Unauthorized”.
 

Access Your Service

I want to set up my ORDS module so it can be accessed by a third party application so I’ll set up OAuth 2.

Create an OAuth 2 Client

Using the OAUTH PL/SQL Package, I will create an OAuth2 client using the privilege I created above.

Then I will grant the new OAUTH2 client the role I created above.

Test

In order to generate an access token, I need to get my client id and secret from the user_ords_clients table.

When you create an OAuth2 client, a REST service ‘/oauth/token’ is created for you that your applications can use to generate a bearer token using the above id and secret.

Notice that this token expires in 3600 seconds.  Once it expires, you would repeat the above call to generate a new token.

Now that I have an access_token I can include it in the Authorization header to access my secure ORDS service.  Notice that since this is a Bearer token I set the Authorization value to ‘Bearer <<my token>>’.

Example Usage

The following is an example of how to make secure REST calls from an external application after you’ve followed the above steps.

On the application server

Store the client_id and client_secret in environment variables.

In your application

Summary

Setting up security on your ORDS modules is quick and fairly easy.

OAuth2 is just one way to access your secured ORDS modules.  If you’d like to setup Basic Auth checkout this post by Jeff Smith.

Console the ORDS documentation for other examples and a much more in-depth explanation.

Information, Learning, PL/SQL, Python

Execute PL/SQL calls with Python and cx_Oracle

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After you’ve got the hang of performing Basic CRUD operations with cx_Oracle you’re ready to start tapping into some of the real power of the Oracle Database.

Why use PL/SQL?

Python is an excellent language for most things you want your application to do, but when you’re processing data it just goes faster if you do the work where the data is.

This post will cover how to execute Oracle PL/SQL functions and procedures using Python and cx_Oracle.  I’m assuming you’re already familiar with PL/SQL if not, you can get some help from Steven Feuerstein and Bryn Llewellyn.  (Additional resources at the end.)

Prerequisites

  • Python 3
  • Oracle Database version 12+
  • Basic Oracle PL/SQL and SQL knowledge.

Setup

If you’d like to follow along with the examples you’ll need to create the following objects in a database schema that is safe to experiment in.  Make sure you have permissions to create the following objects.

To keep everything clean, I’ll be putting my PL/SQL code into a package called pet_manager.

Cleanup

To clean up the database when you are finished with the series, you need to drop the two tables and the package.  Please make sure you’re connected to the correct schema where you created the tables.

Boilerplate template

The template we will be using is:

  1. Install cx_Oracle.
  2. Import the cx_Oracle driver.
  3. Import os module used to read the environment variable.
  4. Get the connection string from the environment variable.
  5. Create the connection object.
  6. Create the cursor object.
I will include this code section with all Python examples and use the connection object “con” and the cursor object “cur” throughout the series.

For each exercise, replace the “# Your code here” line with your code.

Anonymous PL/SQL Block

I’m going to start off with the most basic process and simply execute an anonymous block of PL/SQL code to reset the database tables.

You can execute any DDL or DML statement like this, but if you’re going to run PL/SQL it’s usually best to compile it to the database.

Execute a PL/SQL Procedure

Using the code from the anonymous block I created a procedure in the PL/SQL package called reset_data.

To call this procedure from Python we use the cursor.callproc method and pass in the package.procedure name to execute.

Assuming everything works, there will not be any response.  So this works as a ‘fire and forget’ way to call database procedures.

Pass Parameters

I have a procedure in my PL/SQL package that we can use to create a new pet in the lcs_pets table.  It accepts the pet_name, owner_id and pet_type.  Using these values it will insert a new entry into the lcs_pets table.

Now on the Python side.

I prefer to set my values with variables so that my code is easier to read, so I’ll create and set pet_name, owner_id and pet_type.

Next, I’ll call the cursor.callproc method and add an array containing the values to pass in the order they are defined in the database.

If everything works there will not be any response.

You can also use keyword parameters.  This also makes your code easy to read and also makes it so you don’t need to worry about the order of the parameters.

Once again, if everything works there will not be any response.

Get PL/SQL Function Return Values

When a row is added to the lcs_pets table a new id is automatically generated.  Having this id can be useful so I created a function in my PL/SQL package that will create a new pet in the lcs_pets table, just like in the previous function, but it will return the new id.

Using Python to call a function in the database and get the return value I’ll use the cursor.callfunc method.

  1. I set the variables that I’ll use as arguments to the function.
  2. Define a new_pet_id variable and assign it the value returned from callfunc.
  3. The second argument of the callfunc method is used to define the type of the data being returned.  I’ll set it to int.  (cx_Oracle will handle the NUMBER to int conversion.)
  4. I pass in the array of values just like I did when I used callproc.
  5. Print the returned value for new_pet_id.

Out Parameters

Out parameters can be very handy when you need to pass back more than one piece of information.  I have an add_pet function in the PL/SQL package that will check to see if the pet type you’re adding needs a license or not.  The function will return the new id like before, and a ‘yes’ or ‘no’ through the out parameter.

To work with the out parameter in Python I’ll add a string variable called ‘need_license’.  It can be defined using ‘cursor.var(str)‘. Then we just add the new variable to the values array in the correct position.  This works the same when using out parameters with the callproc method.

To get the value from ‘need_license’ we call it’s getvalue() function.

Accept Argument Values

So far I’ve hard-coded the variable values in the Python code and the methods are fairly simple, so there’s a low chance of errors.  But, for most methods, we want to accept parameter values that can be passed into the Python code then on to the PL/SQL functions.  I’ll modify the Python method to accept command line arguments.

We need to import sys so that we can use sys.argv[] to grab the command line arguments and assign them to the variables.

If I run this to add a dog, I get:

Adding a fish, I get:

PL/SQL Exceptions

Now that I’m accepting outside argument values, the odds that I’ll eventually get errors with the above code is almost a certainty.  If an error happens in the Python code you can handle it as you normally would.  But, what if there’s an error thrown by the PL/SQL code?

It’s easy enough to test this.  Make the same call as before but pass in a string for the second value.

I would recommend that you handle errors as close to where they happen as you can.  In this example, you could catch the error in the PL/SQL function and either handle it or raise it.  If you don’t handle it in PL/SQL it will be passed back to cx_Oracle which will throw a cx_Oracle.DatabaseError.  At that point, you can handle it as you would when any other Error is thrown in your Python application.

Additional Resources

Information, JET, Meetups/Conventions, Python

Track-a-Watt – IoT to the Database: code walkthrough

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This is a companion post to my Track-a-Watt – IoT to the Database presentation.

If I missed you at GLOC 2017, you can still catch it at KScope 2017 or OpenWest 2017.

I’ve packed loads of stuff into this presentation, including: soldering (no software involved), Python, Javascript, HTML, PL/SQL and a little SQL (there has to be at least a little SQL in any application! :-)).

Even if I had a few hours of presentation time, it’d be hard to do justice to all these different scripts in their different languages, without losing lots of my audience somewhere along the way. So the presentation keeps things brief and to the point, and I will use this post to provide more depth for some of the code sections.

Python modules

sensorhistory.py

I mention that there are some names and labels used in this module that reference “5 minutes”.

I didn’t find any instances where a value for 5 minutes (300 seconds) is used in the functionality.  Five minutes is only used as labels and object names.

The declarations for these can be found on lines:

  • 103 – cumulative5mwatthr.
    A variable used to store the cumulative watts per hour readings since the timer was started.  We’ll call this total-watt-hours below.
  • 105 – fiveminutetimer.
    A variable used to store the time when the timer was initialized.  We’ll call this start-time below.
  • 119 – reset5mintimer.
    A function to reset start-time and total-watts.
  • 123 – avgwattover5min.
    A function that prints the current data and returns the calculated average watts per hour since the timer started.
  • 124 – fivetimer.
    A text label in the print statement.
  • 125 – 5mintimer and 5minwatthr
    Labels in the text returned by the __str__ function.

This is just a demo, so I didn’t rename these objects.  I only highlight these in case the names cause confusion after I change the timer to 10 seconds.

xbee.py

I only made one change in this module due to an error I received.  I have been running this project on both Windows 7 and Fedora 25 machines.  On one machine the values for p are passed in as Unicode and the other they are Strings.

The change here just checks to see if p is a String if so, convert it to Unicode otherwise accept it as is.  Thanks, Anthony Tuininga for making this clean and compact.

wattcher.py to wattcher-min.py

The original code for the Tweet-a-Watt project has some functionality that I don’t intend to use for my simple graph.  I created the wattcher-min.py module by stripping out most of these features.

Average Watts/Hour calculation

As far as I can prove with my (cough cough) math skills, the algorithm used to calculate watts per hour works for whatever time slice you want to track.

I have not gone through all of the code that leads up to this point, but as I understand it:

  • The kill-o-watt is collecting a constant stream of readings.
  • The kill-o-watt X-Bee transmits the reading to the computer every 2 seconds where the data is stored in the array, wattdata[].
  • This code calculates and stores the average watts used in the last second.
To calculate the average W/Hr during our current time slice:

  • Calculate the number of seconds since the last reading.
  • Multiply the average watts per second by the elapsed seconds then divide by 3600 (seconds in an hour).
  • Reset the last reading timer.
  • Print the data.
  • Add the calculated average W/Hr for this time slice to the running total.
Here’s a basic explanation:

When a chunk of data comes in, we calculate the average W/Hr for the first second of that chunk.  Multiply that value by the number of seconds since the previous reading.  This gives us the average W/Hr for a 2 second time slice.  If we were to collect those slices for one hour and add them together we would have X watts used in one hour.

The cumulative watts used will continue to accrue until we pass the limit of the timer we’re using to determine how often to send the data up to ORDS.

To calculate the average W/Hr during the last 10 seconds:

  • Multiply the cumulative watts used by 3600 (seconds in an hour).
  • Divide by the seconds since the last time we sent data to ORDS.
The short explanation is if we were getting a consistent reading of 5 watts per hour for every sample, every 10 seconds this calculation would come out to 5 W/Hr during the last 10 seconds.  However, it’s not likely that we will get the same 5 W/Hr every reading so this function will give us the average W/Hr during the last 10 seconds.

I can understand if you’re a bit confused at this point. There seem to be a couple extra steps here than what should be needed for my simple graph.  I had to work out a simulation in a spreadsheet before I could accept that it was working.  However, I left the calculation code alone assuming that it may be needed for some of the more advanced versions of the project.

If your math skills are better than mine and you find that my explanation is wrong or you can explain it better, please leave a comment.

Oracle Jet

The Oracle Jet graph used in the example is the basic Line with Area Chart.  I’m using the Y axis for the W/Hr data and the X axis for the timestamps.

The graph has the capability to track multiple series of data which would be useful for multiple kill-a-watts, but I’m only using one in the presentation.

The relationship between the X and Y axises is positional using the array position for the data elements in two arrays.

JavaScript

This is a typical jQuery ajax GET function.

Inside the success function:

  • Get the items array from the response.
  • Create a variable for the X-axis data.
  • Create a variable for the Y-axis data.  Since we’re only tracking one sensor we can define the name value and initialize an items array for it.
  • Loop through the response items.
  • Populate the items array for our sensor (Y axis).
  • Populate the timestamp array (X axis).
  • Set the ko.observable objects for the two axises of the graph.

Next is a short function to call getData() every 5 seconds.

HTML

We copy the HTML from the cookbook for just the graph component.

Since we’re not using the additional functionality from the Jet Cookbook example we remove the highlighted lines (14, 15).

Go try something new

The goal of this presentation is to encourage people to go out and try something a little out of their comfort zone.  If you think your soldering skills are lacking find a maker group in your area and take a class.  If you are strong in one programming language try another.

This is a great project to experiment with, there are a few different skills all mixed together, each of them is fairly close to entry level and they are popular enough that there should be a lot of help available.

As always, if you run into issues feel free to leave a comment here or hit me up on twitter and I’ll be glad to help get you going.

I plan to update this post as questions arise.  If you’d like to see it all running together catch one of my upcoming sessions.

Information

JDBC Connection to Exadata Express Cloud Database from a Raspberry Pi

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Spoiler Alert: It’s pretty much the same as any other Linux system.

The official documentation can be found on the Oracle website.

Install Linux on your Raspberry Pi

I prefer to use BerryBoot, it makes it real easy to install several flavors of Linux on my pi.  You can get it from their repo.  For this example, I’m using Raspbian.

If you plan to use SSH this is a good guide for setting up passwordless SSH access.

Java Version

Verify that you have the correct Java Version:
JDK 8 – JDK8u71 or higher
JDK 7 – JDK7u80 or higher

When this post was written, Raspbian was using an older version of Java 8 so an upgrade is needed.

There are already quite a few guides out there if you need help.  I used this one.

JCE Files

Next, we need to download and install the JCE Unlimited Strength Jurisdiction Policy Files.

After you download the .zip file, extract the files and place the two .jar files (local_policy.jar & US_export_policy.jar) in
<java-home>/lib/security.

<java-home> refers the home for the JRE not the JDK.  My full path is:
/opt/java/jdk1.8.0_121/jre/lib/security/

Oracle Exadata Express Cloud Database

Now that Linux and Java are setup, it’s time to setup your Oracle Exadata Express Cloud Database.

Log into your Service Console and find the Client Access section.

If client access is not already enabled, you will see a link to Enable Clent Access.  Click that link and follow the instructions.  Once it’s done it will look like this.

Click on Download Client Credentials and you’ll get this popup:

Enter and confirm a password.  This is the password that your JDBC client will use to access your credentials.

Click download then extract the file.  I extracted mine into my home directory in a directory named EE_Credentials.
/home/pi/EE_Credentials

Create a Test Class

Now we have everything in place we can try it out.

In order to ensure that nothing else is interfering with our test, let’s compile a simple test class.

  1. Replace the strings for your user and password.
  2. Save this into a file called testJDBC.java.
  3. Copy the oracle driver into the same directory.  We’ll manually set the classpath to keep our test self-contained.
  4. Compile the class.
    javac testJDBC.java

Required System Properties

The last thing we need to do is set some system properties using the -D option for Java.

The parameters we’ll be using are:

If you’re using JDK7 you’ll also need to include

Remember to replace YourPassword with the password you set above and /home/pi/EE_Credentials with the path you extracted the credentials file into.

To run the test: (all one line)

If you see the error:
Caused by: oracle.net.ns.NetException: could not resolve the connect identifier “dbaccess”
Make sure the path in the properties is where you extracted the credentials file to.  You should see a tnsnames.ora file in there.

Use Environment Variables

If everything worked then we can make it a bit easier by moving those properties to an environment variable.

Then run it with:

Now we can be confident that we can connect to and query from the Oracle Exadata Express Cloud Database.

To use the connection in your other applications, follow these instructions and read the documentation on setting the Java properties.

For example:
If you’re using Liquibase, set the environment variable like in the example above.  If you’re using OpenHab the environment variable would be named EXTRA_JAVA_OPTS.

Connecting to Oracle Exadata Express Cloud Database is easy and it provides a secure reliable database to support your applications.

Information, Learning, Ruby

Delete (cruD) using Ruby-OCI8

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In this post, we’re going to take a look at the D in CRUD: Delete.

We use the ruby-oci8 driver to delete some data in the database tables, using the connection object created in the Initial Setup section of the first post in this series.

PLEASE REVIEW ALL EXAMPLE CODE AND ONLY RUN IT IF YOU ARE SURE IT WILL NOT CAUSE ANY PROBLEMS WITH YOUR SYSTEM.

Helper Function

My helper function get_all_rows() encapsulates a select statement used to verify that the deletes worked. The select functionality is covered in the R part of this series, so I won’t go into the details here.

Add this function to the top of your file.

Resetting the data

To keep the examples clean and precise, I will reset the data at times.

Create a new file called reset_data.rb with the following code and run it whenever you would like to reset the data. (Notice this version adds people and pet data not included in other sections.)

Boilerplate template

The template we will be using is:

For each exercise, replace the “# Your code here” line with your code.

Reset the data

First, let’s run reset_data.rb to set up our data.

Simple delete

We will perform a simple delete that removes a single record from the lcs_people table.  These are the steps performed in the code snippet below.

  • Prepare a SQL DELETE statement, deleting the record with an id of 1.
  • Parse the statement to create a cursor.
  • Bind the id value.  (See the R part of this series for an explanation of bind variables.)
  • Execute the statement.
  • Commit the transaction.
When I run this code in my Ruby session, I see:

Extra Fun 1

Delete all the birds.

Your results should be:

Answer

Reset the data

Now is a good time to run reset_data.rb.

Boilerplate change

Change the boilerplate get_all_rows statements to get people and pet data.

Deleting records referenced by Foreign Keys

If you are using integrity constraints in your database (of course you are, because then you let the database do some heavy lifting for you), you will sometimes need to change the way you process your changes.

In our design, we have a Foreign Key constraint in lcs_pets that ensures if a pet has an owner, that owner exists.

This is the statement that creates the constraint in the Creating the Database Objects section of the Initial Setup post.

If we attempt to delete a record in lcs_people that is referenced in lcs_pets (Person has a pet,) we get an error.

When I run this code in my Ruby session, I see:

Before deleting the person you have to handle the pet (watch out for claws and teeth).

There are a few options here, depending on your database design:

  • If: pets are not required to have an owner and you only want to delete the person, not the pets.  Then: you can update the pets and set their owner to null.
  • If: pets are required to have an owner.  Then: you can delete the pets for the owner.

In either of the above scenarios, you can update the pets and set their owner to another person.

Bob is moving out of our area and his new apartment doesn’t allow pets, so he’s giving them to Kim.  Let’s use that last option here.

  • Prepare a SQL UPDATE statement, changing owner to 2 (Kim) for the records with an owner of 1 (Bob).  Updating is covered in the U part of this series.
  • Parse the statement to create a cursor.
  • Bind the new and old owner values.
  • Execute the statement.
  • Prepare a SQL DELETE statement, deleting records with an id of 1 (Bob).
  • Parse the statement to create a cursor.
  • Bind the id value.
  • Execute the statement.
  • Commit both transactions.
When I run this code in my Ruby session, I see:

When you change data it’s a good idea to verify the number of affected rows.  This is covered in the R part of this series.

Extra Fun 2

Due to a zoning change, snakes are no longer allowed in our area.  Stacey has decided to move and take Sneaky with her.

Let’s fix our data.

Your results should be:

Answer

Some other things you could try
  • Change the database constraints to delete or Null the child record on delete (a cascading delete).  Delete a person and let the database handle the children.
  • Remove the people who don’t have any pets.

Series sections

Initial Setup
Create records
Retrieve records
Update records
Delete records

Information, Learning, Perl

Delete (cruD) using Perl and DBD::ORACLE

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In this post, we’re going to take a look at the D in CRUD: Delete.

We use the DBD::Oracle driver to delete some data in the database tables, using the connection object created in the Initial Setup section of the first post in this series.

PLEASE REVIEW ALL EXAMPLE CODE AND ONLY RUN IT IF YOU ARE SURE IT WILL NOT CAUSE ANY PROBLEMS WITH YOUR SYSTEM.

Helper Function

My helper function get_all_rows encapsulates a select statement used to verify that the deletes worked. The select functionality is covered in the R part of this series, so I won’t go into the details here.

Add this function to the top of your file.

Resetting the data

To keep the examples clean and precise, I will reset the data at times.

Create a new file called reset_data.perl with the following code and run it whenever you would like to reset the data. (Notice this version adds people and pet data not included in other sections.)

Boilerplate template

The template we will be using is:

For each exercise, replace the “# Your code here” line with your code.

Reset the data

First, let’s run reset_data.perl to set up our data.

Simple delete

We will perform a simple delete that removes a single record from the lcs_people table.  These are the steps performed in the code snippet below.

  • Prepare a SQL DELETE statement, deleting the record with an id of 1.
  • Bind the id value. (See the R part of this series for an explanation of bind variables.)
  • Execute the statement.
When I run this code in my Perl session, I see: