Database Schema Declaration

Cycle/Database ships with an included mechanism to declare table structures, FKS and indexes using declarative approach and schema comparison.

Practically, table changes can be executed using an external migration system.

#Principle of Work

Before any operation/declaration can be applied to the table schema, DBAL will load the currently existing structure from the database and normalize it into internal format.

As a result, you are allowed to apply the modification to the table schema using a declarative way instead of an imperative one. Once schema save is requested, DBAL will generate a set of creation and altering operations based on the difference between the declared and existing schemas.

See below how to use Cycle\Database\Schema\Reflector to sync multiple related tables.

#To Start

To get an instance of AbstractTable use a similar way as described in Schema Introspection (make sure your read them first).

No need to check for table existence.

protected function indexAction(\Cycle\Database\Database $database)
{
    $schema = $database->table('new_table')->getSchema();

    // Schema is supposed to be empty
    var_dump($schema);
    var_dump($schema->exists());
}

#Columns and Abstract Types

You can add columns to a specific schema by simply setting their type. Use the following example to start:

$schema = $database->table('new_table')->getSchema();

$schema->column('id')->primary();
$schema->column('name')->string(64); //String length 64 characters
$schema->column('email')->string();  //Default string length is 255 symbols
$schema->column('balance')->decimal(10, 2);
$schema->column('description')->text();

All of the listed methods are added into the table and column doc comments so your IDE/editor will highlight them.

Use the shorter version if you find it easier:

$schema = $database->table('new_table')->getSchema();

$schema->primary('id');
$schema->string('name', 64); //String length 64 characters
$schema->string('email');    //Default string length is 255 symbols
$schema->decimal('balance', 10, 2);
$schema->text('description');

To create the table schema in the database we have to call the method save of our AbstractTable:

$schema->save();

Depending on which database driver you are using, DBAL will generate different SQL statements to create a table:

CREATE TABLE `primary_new_table` (
    `id` int (11) NOT NULL AUTO_INCREMENT,
    `name` varchar (64) NULL,
    `email` varchar (255) NULL,
    `balance` decimal (10, 2) NULL,
    `description` text NULL,
    PRIMARY KEY (`id`)
) ENGINE = InnoDB

Note that database prefix has been addressed automatically.

In Postgres the create syntax will look like:

CREATE TABLE "secondary_new_table" (
    "id" serial NOT NULL,
    "name" character varying (64) NULL,
    "email" character varying (255) NULL,
    "balance" numeric (10, 2) NULL,
    "description" text NULL,
    PRIMARY KEY ("id")
)

Note, by default every column is created as nullable. Use the nullable method to overwrite it (see below).

Once the schema is created you can add new columns into it by only declaring them in your code:

$schema = $database->table('new_table')->getSchema();

$schema->primary('id');
$schema->string('name', 64); //String length 64 characters
$schema->string('email');    //Default string length is 255 symbols
$schema->decimal('balance', 10, 2);

$schema->longText('description'); //New type
$schema->integer('count_visits'); //New column

$schema->save();

DBAL will detect 2 new declarations being added and generate appropriate code:

ALTER TABLE `primary_new_table` CHANGE `description` `description` longtext NULL;
ALTER TABLE `primary_new_table` ADD COLUMN `count_visits` int (11) NULL;

Attention, not every type can be easily changed in some databases. Make sure you are not violating DBMS specific cross-type conversion (string => integer for example).

#Abstract Types

As you can notice, DBAL uses a set of "abstract" (common for all DBMS) types to declare table columns. Internally such types are mapped to appropriate internal DBMS column type.

Attention, in some cases the type returned by ColumnSchema->abstractType() might not be the same as declared one, such problem may occur in cases when DBMS uses the same internal type for multiple abstract types (for example most of the databases does not differentiate long/short/medium text and binary types).

However, this does not break anything in schema synchronization as DBAL creates operations based on the difference in internal database types, not based on the declared abstract one.

#Enum Type

The Enum type only exists natively in the MySQL database, in other DBMS it will be emulated using string type with associated constrain. To define enum type you have to list it's values:

$schema->column('status')->enum(['active', 'disabled']);

//Alternative definition
$schema->enum('statusB', ['active', 'disabled']);

As in other cases declared schema will be synced will database one, so you can add and remove enum values at any moment.

#Default values

It's recommended to set a default value for enum and some other columns. This can be performed using defaultValue():

$schema->column('status')->enum(['active', 'disabled'])->defaultValue('disabled');
$schema->enum('status_b', ['active', 'disabled'])->defaultValue('active');

And again, you can change the default value at any moment. If you wish to drop the default value simple set the method argument as null.

$schema->enum('statusB', ['active', 'disabled'])->defaultValue(null);

#Nullable columns

To set column as NOT NULL use nullable method with false as parameter:

$schema->string('name', 64)->nullable(false);

You can change NULL/NOT NULL flag at any moment you want. Additionally, you can try to combine NOT NULL column with the non-empty default value, this will allow you to add new columns to the non-empty table.

$schema->integer('new_column')->nullable(false)->defaultValue(0);

ORM will automatically resolve default value for NOT NULL casted columns.

#Primary Index

Table primary index can be set only while creation. DBAL will set PK automatically based on the column with type "primary" or "bigPrimary" declared in your schema.

To declare compound or custom primary keys, use table method setPrimaryKeys().

$schema->primary('id');
$schema->string('something', 16);
$schema->setPrimaryKeys(['id', 'something']);

You are not able to change primary keys after the table being created.

#Indexes

Use methods index to declare indexes, array of column names is required:

$schema = $database->table('other_table')->schema();

$schema->primary('id');
$schema->string('name', 64)->nullable(false);

$schema->string('email');

$schema->index(['email']); //Simple index
$schema->column('email')->index(); //You can also use alternative declaration for simple indexes

$schema->index(['name', 'email']); //Compound index

$schema->save();

If you wish to add unique index you can change your code a little bit:

$schema->column('email')->unique(); //Simple unique index
$schema->index(['name', 'email'])->unique(true);  //Compound unique index

You can make index non unique at any moment:

$schema->index(['name', 'email'])->unique(false);

Attention, you can not add indexes to text or binary columns. You have to remember about limitations current DBMS applies to its indexes. For example, you can not create a unique index for the non-empty table with invalid (from the standpoint of the index) data. Some databases also have a maximum index size and etc.

#Foreign Keys

You can link tables together by using FKs:

$first = $database->table('first')->getSchema();

$first->primary('id');
$first->string('name', 64);
$first->string('email');

$first->save();

$second = $database->table('second')->getSchema();

$second->bigPrimary('id');
$second->string('title');

$second->save();

In order to create FK we have to define local column and call foreign method on it:

$second->integer('first_id');
$second->foreign('first_id')->references('first', 'id');

If we using MySQL connection DBAL will generate following SQL:

ALTER TABLE `primary_second` ADD COLUMN `first_id` int (11) NULL;
ALTER TABLE `primary_second` ADD CONSTRAINT `primary_second_foreign_first_id_55f205f594a3a` FOREIGN KEY (`first_id`) REFERENCES `primary_first` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION;

You can define custom DELETE and UPDATE rules for your FK:

$foreignKey = $second->foreign('first_id')->references('first', 'id');

$foreignKey->onDelete(\Cycle\ORM\Reference\ReferenceInterface::CASCADE);
$foreignKey->onUpdate(\Cycle\ORM\Reference\ReferenceInterface::CASCADE);

Now, when the record in "first" table will be removed related data from the "second" table will be wiped also. You can read more about different actions here.

Please note that not every DBMS support actions outside of NO ACTION and CASCADE. In addition, some databases (hi, Microsoft) may forbid multiple foreign keys with CASCADE action in one table to avoid a reference loop.

#Rename Schemas

You can rename column in existed table by simply giving it new name or via shortcut method:

$schema->string('email')->setName('new_email');

$schema->renameColumn('email', 'new_email');

Call save method of AbstactTable to save your changes.

Use similar approach to rename indexes and table name.

$schema->setName('new_table_2');
$schema->save();

#Drop columns and indexes

Use methods dropColumn, dropIndex and dropForeign to remove elements:

$schema->dropColumn('new_email');
$schema->save();

To drop table call declareDropped method of your schema prior to save:

$schema->declareDropped();
$schema->save();

#Clean Table schema

In some cases you might want table schema strictly follow declared elements and automatically delete all non-declared columns:

$schema->setState(null);

Now you are able to redefine table schema.

#Work with Comparator

To get access to table state comparator use getComparator method of your schema:

dump($schema->getComparator()->addedColumns());

You can use comparator to generate migrations instead of letting DBAL sync your schemas.

#Sync multiple Tables

In some cases you might want to create multiple linked tables. In order to handle such operation feed your table schemas into Cycle\Database\Schema\Reflector:

$schema = $database->table('table_a')->getSchema();
$schema->primary('id');

$schemaB = $database->table('table_b')->getSchema();
$schemaB->primary('id');
$schemaB->integer('a_id');
$schemaB->foreign('a_id')->references('table_a', 'id');

$r = new \Cycle\Database\Schema\Reflector();
$r->addTable($schemaB);
$r->addTable($schema);

$pool->run();

Cycle\Database\Schema\Reflector will sort your tables based on their cross dependencies.