Laravel5.1 Learning Note 17 Database 3 Data Migration

• Introduction
• Generating migrations
• Migration Structure
• Running Migrations
  • Rolling back migrations
• Writing Migrations
  • Creating Tables
  • Renaming/dropping Tables
  • Creating Columns
  • modifying Columns
  • Dropping Columns
  • Creating Indexes
  • Dropping Indexes
  • Foreign Key Constraints

Introduction

Migrations is like version control for your database, allowing a team to easily modify and share the application ' s Databa SE schema. Migrations is typically paired with Laravel's schema builder to easily build your application ' s database schema.

The Laravel Schema facade provides database agnostic support for creating and manipulating tables. It shares the same expressive, fluent API across all of Laravel ' s supported database systems.

Generating migrations

To create a migration, use the make:migration Artisan command:

php artisan make:migration create_users_table

The new migration is placed in your database/migrations directory. Each migration file name contains a timestamp which allows Laravel to determine the order of the migrations.

The and options may also is used to indicate the name of the table and whether the migration would be --table --create creating A new table. These options simply pre-fill the generated migration stub file with the specified table:

php artisan make:migration add_votes_to_users_table --table=usersphp artisan make:migration create_users_table --create=users

Migration Structure

A Migration class contains-methods: up and down . The up method is used to add new tables, columns, or indexes to your database, while the down method should simply Rev Erse the operations performed by the up method.

Within both of these methods you could use the Laravel schema Builder to expressively create and modify tables. To learn about all of the methods available on Schema the builder and check out its documentation. For example, let's look at a sample migration that creates a flights table:

<?phpuse Illuminate\Database\Schema\Blueprint;use Illuminate\Database\Migrations\Migration;class CreateFlightsTable extends Migration{    /**     * Run the migrations.     *     * @return void     */    public function up()    {        Schema::create(‘flights‘, function (Blueprint $table) {            $table->increments(‘id‘);            $table->string(‘name‘);            $table->string(‘airline‘);            $table->timestamps();        });    }    /**     * Reverse the migrations.     *     * @return void     */    public function down()    {        Schema::drop(‘flights‘);    }}

Running Migrations

To run all outstanding migrations for your application, use the migrate Artisan command. If you are using Thehomestead Vsan, you should run the this command from within your VM:

php artisan migrate

If you receive a ' class not found ' error when running migrations, try running the composer dump-autoload command and re-issuing the migrate Command.

Forcing migrations to Run in Production

Some migration operations is destructive, meaning they may cause your to lose data. In order to protect the running these commands against your production database, you'll be a prompted for Confirmatio n before these commands is executed. To force the commands-run without a prompt, use the --force flag:

php artisan migrate --force

Rolling back migrations

To rollback the latest migration "operation", your may use the rollback command. Note that this Rolls-the last "batch" of migrations-ran, which may include multiple migration files:

php artisan migrate:rollback

The command would roll back all of migrate:reset your application ' s migrations:

php artisan migrate:reset

Rollback/migrate in single Command

The command would first roll migrate:refresh to your database migrations, and then run the migrate command. This command effectively re-creates your entire database:

php artisan migrate:refreshphp artisan migrate:refresh --seed

Writing Migrations

Creating Tables

To create a new database table with the method on the create Schema facade. The create method accepts the arguments. The first is the name of the table and while the second are a Closure which receives a Blueprint object used to define the new table :

Schema::create(‘users‘, function ($table) {    $table->increments(‘id‘);});

Of course, when creating the table, your may use any of the schema Builder's column methods to define the table ' s columns.

Checking for Table/column existence

Easily check for the existence of a table or column using the and hasTable hasColumn methods:

if (Schema::hasTable(‘users‘)) {    //}if (Schema::hasColumn(‘users‘, ‘email‘)) {    //}

Connection & Storage Engine

If you want to perform a schema operation on a database connection that's not your default connection, use the connection metho D:

Schema::connection(‘foo‘)->create(‘users‘, function ($table) {    $table->increments(‘id‘);});

To set the storage engine for a table, set the property on the engine schema Builder:

Schema::create(‘users‘, function ($table) {    $table->engine = ‘InnoDB‘;    $table->increments(‘id‘);});

Renaming/dropping Tables

To rename a existing database table, use the rename method:

Schema::rename($from, $to);

To drop a existing table, you could use the drop or dropIfExists methods:

Schema::drop(‘users‘);Schema::dropIfExists(‘users‘);

Creating Columns

To update an existing table, we'll use the table method on the Schema facade. Like create the method, the table method accepts-arguments:the name of the table and a that Closure receives a Blueprint inst Ance we can use to add columns to the table:

Schema::table(‘users‘, function ($table) {    $table->string(‘email‘);});

Available Column Types

Of course, the schema Builder contains a variety of column types that is use when building your tables:

Command
Description

$table->bigIncrements(‘id‘);
Incrementing ID using a "big integer" equivalent.

$table->bigInteger(‘votes‘);
BIGINT equivalent for the database.

$table->binary(‘data‘);
BLOB equivalent for the database.

$table->boolean(‘confirmed‘);
BOOLEAN equivalent for the database.

$table->char(‘name‘, 4);
CHAR equivalent with a length.

$table->date(‘created_at‘);
DATE equivalent for the database.

$table->dateTime(‘created_at‘);
DATETIME equivalent for the database.

$table->decimal(‘amount‘, 5, 2);
DECIMAL equivalent with a precision and scale.

$table->double(‘column‘, 15, 8);
DOUBLE equivalent with precision, digits in total and 8 after the decimal point.

$table->enum(‘choices‘, [‘foo‘, ‘bar‘]);
ENUM equivalent for the database.

$table->float(‘amount‘);
FLOAT equivalent for the database.

$table->increments(‘id‘);
Incrementing ID for the database (primary key).

$table->integer(‘votes‘);
The INTEGER equivalent for the database.

$table->json(‘options‘);
JSON equivalent for the database.

$table->jsonb(‘options‘);
JSONB equivalent for the database.

$table->longText(‘description‘);
Longtext equivalent for the database.

$table->mediumInteger(‘numbers‘);
Mediumint equivalent for the database.

$table->mediumText(‘description‘);
Mediumtext equivalent for the database.

$table->morphs(‘taggable‘);
Adds INTEGER and taggable_id STRING taggable_type .

$table->nullableTimestamps();
Same timestamps() as, except allows NULLs.

$table->rememberToken();
Adds as remember_token VARCHAR (+) NULL.

$table->smallInteger(‘votes‘);
SMALLINT equivalent for the database.

$table->softDeletes();
Adds deleted_at column for soft deletes.

$table->string(‘email‘);
VARCHAR equivalent column.

$table->string(‘name‘, 100);
VARCHAR equivalent with a length.

$table->text(‘description‘);
TEXT equivalent for the database.

$table->time(‘sunrise‘);
Time equivalent for the database.

$table->tinyInteger(‘numbers‘);
TINYINT equivalent for the database.

$table->timestamp(‘added_on‘);
TIMESTAMP equivalent for the database.

$table->timestamps();
Adds created_at and updated_at columns.

Column Modifiers

In addition to the column types listed above, there is several other column ' modifiers ' which you could use while adding th E column. For example, the-to-make the column "nullable", the nullable method:

Schema::table(‘users‘, function ($table) {    $table->string(‘email‘)->nullable();});

Below is a list of all the available column modifiers. This list does not include the index modifiers:

Modifier
Description

->first()
Place the column ' first ' in the table (MySQL only)

->after(‘column‘)
Place the column ' after ' another column (MySQL only)

->nullable()
Allow NULL values to is inserted into the column

->default($value)
Specify a "default" value for the column

->unsigned()
Set integer Columns toUNSIGNED

modifying columnsprerequisites

Before modifying a column, be sure to add the doctrine/dbal dependency to your composer.json file. The Doctrine Dbal Library is used to determine the current state of the the column and create the SQL queries needed to make T He specified adjustments to the column.

Updating Column Attributes

changeThe method allows modify an existing column to a new type, or modify the column ' s attributes. For example, you could wish to increase the size of a string column. changeto see the method in action, let's increase the size of the name column from 50:

Schema::table(‘users‘, function ($table) {    $table->string(‘name‘, 50)->change();});

We could also modify a column to be nullable:

Schema::table(‘users‘, function ($table) {    $table->string(‘name‘, 50)->nullable()->change();});

Renaming Columns

To rename a column, the method on the renameColumn Schema Builder. Before renaming a column, be sure to add the doctrine/dbal dependency to your composer.json file:

Schema::table(‘users‘, function ($table) {    $table->renameColumn(‘from‘, ‘to‘);});

Note: Renaming columns in a table with a enum column was not currently supported.

Dropping Columns

To drop a-column, use the method on the dropColumn Schema Builder:

Schema::table(‘users‘, function ($table) {    $table->dropColumn(‘votes‘);});

You could drop multiple columns from a table by passing an array of column names to the dropColumn method:

Schema::table(‘users‘, function ($table) {    $table->dropColumn([‘votes‘, ‘avatar‘, ‘location‘]);});

Note: Before dropping columns from a SQLite database, you'll need to add the doctrine/dbal dependency to your composer.json file and run the c4/> command in your terminal to install the library.

Creating Indexes

The schema builder supports several types of indexes. First, let's look at the A example that specifies a column ' s values should is unique. To create the index, we can simply chain the unique method onto the column definition:

$table->string(‘email‘)->unique();

Alternatively, you could create the index after defining the column. For example:

$table->unique(‘email‘);

Even pass an array of columns to an index method to create a compound index:

$table->index([‘account_id‘, ‘created_at‘]);

Available Index Types

Command
Description

$table->primary(‘id‘);
ADD a primary key.

$table->primary([‘first‘, ‘last‘]);
ADD composite keys.

$table->unique(‘email‘);
ADD a unique index.

$table->index(‘state‘);
ADD a basic index.

Dropping Indexes

To drop a index, you must specify the index ' s name. By default, Laravel automatically assigns a reasonable name to the indexes. Simply concatenate the table name, the names of the column in the index, and the index type. Here is some examples:

Command
Description

$table->dropPrimary(‘users_id_primary‘);
Drop a primary key from the "Users" table.

$table->dropUnique(‘users_email_unique‘);
Drop a unique index from the "Users" table.

$table->dropIndex(‘geo_state_index‘);
Drop a basic index from the "Geo" table.

Foreign Key Constraints

Laravel also provides support for creating foreign key constraints, which is used to force referential integrity at the D Atabase level. For example, let's define a column on the user_id posts table that references the id column on a users table:

Schema::table(‘posts‘, function ($table) {    $table->integer(‘user_id‘)->unsigned();    $table->foreign(‘user_id‘)->references(‘id‘)->on(‘users‘);});

Also specify the desired action for the ' on delete ' and ' on Update ' properties of the constraint:

$table->foreign(‘user_id‘)      ->references(‘id‘)->on(‘users‘)      ->onDelete(‘cascade‘);

To drop a foreign key, you may use the dropForeign method. Foreign key constraints use the same naming convention as indexes. So, we'll concatenate the table name and the columns in the constraint then suffix the name with "_foreign":

$table->dropForeign(‘posts_user_id_foreign‘);

Laravel5.1 Learning Note 17 Database 3 Data Migration