Last modified 11 months ago

Existing Databases

The following topics are targeted for developers who already have a working database solution in place, but would like to use Propel to work with the data.

Propel provides a number of targets, which are essentially functions in the Phing (XML) build file, to make it easy to work with existing data.

Important Note

Propel 1.3 offers two options for reverse engineering databases:

You can use the new (beta-quality!) "reverse" target which uses Propel's own reverse engineering classes or
You can continue to use the "creole" target which requires you have Creole installed and that you use a special Creole-style DSN pointing to your database.

Before You Get Started

Before you attempt to import an existing database, you should make sure that Propel is properly installed. The Installation chapter of the User Guide? provides a walk-through on getting Propel installed. If you are planning to use Creole for reverse engineering, make sure you have also installed the optional Creole package.

This document will describe how to work with existing databases if you are using the PEAR-installed form of Propel (which is the assumed default). You can certainly apply these instructions to other more advanced installations of Propel (e.g. from SVN).

This examples in this document are for unix/Linux operating systems; however, these instructions should translate easily to Windows.

Working with Database Structures

Propel uses an abstract XML schema file to represent databases. Propel builds the SQL specific to a database based on this schema. Propel also provides a way to reverse-engineer the generic schema file based on database metadata. Propel can optionally use the Creole package's reverse-engineering functionality for this task or its own build-in "schema parser" code (which for 1.3 is based very closely on the Creole code).

Creating an XML Schema from DB Structure

(New) Using Propel's Reverse

Note: the reverse engineering classes may not be able to provide the same level of detail for all databases. In particular, metadata information for SQLite is often very basic since SQLite is a typeless database.

To generate a schema file, create a new directory for your project & specify the connection information in your build.properties file for that project. For example, to create a new project, legacyapp, follow these steps:

Create the legacyapp project directory anywhere on your filesystem:
```
$> mkdir legacyapp
$> cd legacyapp
```

Create a build.properties file in legacyapp dir with the DB connection parameters for your existing database, e.g.:

propel.project = legacyapp

# The Propel driver to use for generating SQL, etc.
propel.database = mysql

# This must be a PDO DSN
propel.database.url = mysql:dbname=legacyapp
propel.database.user = root
# propel.database.password =

Run the reverse target to generate the schema.xml:
```
$> propel-gen ./ reverse
```
Pay attention to any errors/warnings issued by Phing during the target execution and then examine the generated schema.xml file to make any corrections needed.
You're done! Now you have a schema.xml file in the legacyapp project directory. You can now run the default Propel build to generate all the classes.

The generated schema.xml file should be used as a guide, not a final answer. There are some datatypes that Propel may not be familiar with; also some datatypes are simply not supported by Propel (e.g. arrays in PostgreSQL). Unfamiliar datatypes will be reported as warnings and substituted with a default VARCHAR datatype.

Using Creole

The creole target of the Propel build file is designed specifically to generate a schema based on an existing database. This target uses the metadata classes from the Creole db abstraction layer to provide information about the database.

Note: the Creole metadata classes may not be able to provide the same level of detail for all databases. In particular, metadata information for SQLite is often very basic since SQLite is a typeless database.

Create the legacyapp project directory anywhere on your filesystem:
```
$> mkdir legacyapp
$> cd legacyapp
```

Create a build.properties file in legacyapp dir with the DB connection parameters for your existing database, e.g.:

propel.project = legacyapp

# The Propel driver to use for generating SQL, etc.
propel.database = mysql

# This must be a Creole DSN (not PDO!)
propel.database.creole.url = mysql://root@localhost/legacyapp

Run the creole target to generate the schema.xml:
```
$> propel-gen ./ creole
```
Pay attention to any errors/warnings issued by Phing during the target execution and then examine the generated schema.xml file to make any corrections needed.
You're done! Now you have a schema.xml file in the legacyapp project directory. You can now run the default Propel build to generate all the classes.

Migrating Structure to a New RDBMS

Because Propel has both the ability to create XML schema files based on existing database structures and to create RDBMS-specific DDL SQL from the XML schema file, you can use Propel to convert one database into another.

To do this you would simply:

Follow the steps above to create the schema.xml file from existing db.
Then you would change the target database type and specify connection URL for new database in project build.properties file:
```
propel.database = pgsql
propel.database.url = pgsql://unix+localhost/newlegacyapp
```
And then run the sql build target to generate the new DDL:
```
$> propel-gen ./ sql
```
And (optionally) the insert-sql target to create the new database:
```
$> propel-gen ./ insert-sql
```

Working with Database Data

Propel also provides several targets to aid in working with database data. The most important of these are datadump and datasql. The first dumps data to XML and the second converts the XML data dump to a ready-to-insert SQL file.

Important: Both of these targets require that you already have generated the schema.xml for your database.

Dumping Data to XML

Once you have created (or reverse-engineered) your schema.xml file, you can run the datadump task to dump data from the database into a data.xml file.

For example, in the course of running the bookstore-test.php script, data is added to the database. If we were to take a snapshot before the cleanup operations happened, we would have data in the tables. To output the data to the data.xml file, we would execute:

$> propel-gen ./ datadump

In the publisher table we have a row like this:

publisher_id	name
1	William Morrow

In the generated data.xml file, that row would be represented like this:

<dataset name="all">
 ...
  <Publisher PublisherId="1" Name="William Morrow"/>
 ...
</dataset>

Creating SQL from XML

To create the SQL files from the XML, run the datasql task:

$> propel-gen ./ datasql

The generated SQL is placed in the build/sql/ directory and will be inserted when you run the insert-sql target.

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