Insert (Crud) using Perl and DBD::ORACLE

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

We will be using the DBD::Oracle driver to create 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

I will be using a helper function get_all_rows(). This is a select statement used to verify that the inserts 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 then run it whenever you would like to reset the data.

Boilerplate template

The template we will be using is:

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

Simple insert

We will perform a simple insert that adds a single record into the lcs_people table.  These are the steps performed in the code snippet below.

  • Prepare a SQL INSERT statement, specifying the table and columns to insert the data.
  • Bind the three parameters to their values.  (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:

You’ll notice in the bullet points above, I did not commit.  The DBD::Oracle driver is set to auto commit by default.  If you plan to process multiple dependent transactions you may want to disable AutoCommit.

What is a transaction?

When you execute Data Manipulation Language or DML statements, such as the insert I use in this post, those changes are only visible to your current connection or session.

Those changes will not be visible to other sessions (even another session connected to the same schema in which the changes were made) until you commit your changes. That step makes it “permanent” in the database, and available for everyone else to see (and possibly change in a future transaction).  This also allows you to roll back a series of uncommitted transactions if one of the later transactions fails and it would cause data problems for the previous transactions.

Extra Fun 1 & 2

1.  Insert more than 1 row .

Using data for ‘Rob’, 37, ‘I like snakes’ and ‘Cheryl’, 41, ‘I like monkeys’ Your results should be:

Answer

2.  Verify that a second connection cannot see your changes till after the commit.

Using data for ‘Suzy’, 31, ‘I like rabbits’ and assuming that you did the previous exercise your results should be:

Notice that after the insert, the connection that made the insert can see Suzy but the second connection can’t.

After the commit, both connections see Suzy.

Answer
Reset the data

Now is a good time to run reset_data.perl.

Using Identity Columns

You may have noticed that the id column is not passed in, but is automatically set sequentially.  Prior to Oracle Database 12c, this was accomplished using a sequence and a trigger.

In 12c, this can be accomplished by using an Identity Column.

 You can find more information on identity columns here(pdf).
Returning data after an insert
 Sometimes we need to perform additional operations after an insert using data generated by the database, such as the identity column above.  For example, let’s add a person and a pet for them.

We could run an insert then select the value back using the name.  But if the name is not unique we’ll have a problem.  This is where the RETURNING clause is helpful.

We will perform an insert that adds a single record into the lcs_people table. Then using the returned id we will add a pet.  These are the steps performed in the code snippet below.

  • Prepare a SQL INSERT statement, specifying the table and columns to insert the people data.
  • Bind the three “values” parameters to their values.
  • Bind the id parameters to a new variable $new_id using bind_param_inout .
  • Execute the statement returning the id into new_id.
  • Prepare a SQL INSERT statement, specifying the table and columns to insert the pet data.
  • Bind the id parameter to the $new_id value.
  • Execute the statement.
  • Print the new_id value.
  • Prepare a SQL statement.
  • Bind the owner parameter to the $new_id value.
  • Execute the statement.
  • Print the results with a little decoration text.
When I run this code in my Perl session, I see:

Notice the new value, the owner in Sandy’s pets and Sandy’s id in the New Data are all 3 .

Extra Fun 3

3.  Insert Sandy again but return her id and name.

Your results should be:

Notice that (3, ‘Sandy’..) is still there along with our new (4, ‘Sandy’..) but the returned id is 4.  It should return the new id each time you run it.

Answer
 Reset the data

Now is a good time to run reset_data.perl.

Insert more than 1 row

As mentioned above, when you want to insert multiple rows, running multiple insert statements is inefficient and makes multiple trips to the database so instead, we will use execute_array.  In some databases, execute_array is simply a shortcut that will call execute for each record.  However, if your database is capable of bulk processing like Oracle is, the driver will create a much more efficient bulk transaction.

We will perform an insert that adds two records into the lcs_people table.  These are the steps performed in the code snippet below.

  • Create an array for the each column populated with the data for that column.  The longest array will be used to determine the number of transactions if there are any shorter arrays they will be padded with NULL.
  • Prepare a SQL INSERT statement, specifying the table and columns to insert the people data.  Notice we’re using positional bind variables this time.
  • Use execute_array to execute the  statement.  We aren’t accessing any of the execute_array attributes “{}.” Bind the three arrays in order of use.
  • Print the number of records inserted using $tuples, if $tuples is unknown the transaction failed.
When I run this code in my Perl session, I see:

Some things you could try
  • Loop through an array of people and insert each one returning its id.  Using that id add multiple pets with execute_array.
  • Create a large array of people.  Time the difference between looping through single inserts and using execute_array.

Series sections

Initial Setup
Create records
Retrieve records
Update records
Delete records

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