Working With 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. For this case, Propel provides a number of command-line utilities helping with migrations of data and data structures.
Working with Database Structures
Propel uses an abstract XML schema file to represent databases (the schema). 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.
Creating an XML Schema from a DB Structure
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
legacyappproject directory anywhere on your filesystem:
$ mkdir legacyapp $ cd legacyapp
- Create a
legacyapp/directory 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
reversetask to generate the
$ propel reverse
Pay attention to any errors/warnings issued during the task execution and then examine the generated
schema.xmlfile to make any corrections needed.
You're done! Now you have a
schema.xmlfile in the
legacyapp/project directory. You can now run the default Propel build to generate all the classes.
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.
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.
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.xmlfile from existing db.
- Then you would change the target database type and specify connection URL for new database in the project's
propel.database = pgsql propel.database.url = pgsql://unix+localhost/newlegacyapp
- And then run the
sql:buildtask to generate the new DDL:
$ propel sql:build
- And (optionally) the
sql:inserttask to create the new database:
$ propel sql:insert
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