Configure declarative schema

Before Adobe Commerce and Magento Open Source 2.3, extension developers were required to write code (PHP scripts) to change the database schema. The following types of scripts existed before 2.3:

Each script iteratively adds changes. During the installation process, upgrade scripts apply only those changes that have not been applied yet. For example, if you have a module with version 2.1.8 installed and the latest version is 2.1.11, then the upgrade script changes for 2.1.9, 2.1.10, and 2.1.11 will be applied, in order, when you upgrade to 2.1.11. Each upgrade script is responsible for checking the required version for each change to apply. The Adobe Commerce or Magento Open Source installation only knows that a module has an upgrade script, not what versions it affected. That procedure is called migration setup or migration scripts.

The main disadvantage of this approach is that the application applies changes blindly. For example, in one version a new database column might be introduced, only to be removed in the next. Declarative setup eliminates this type of unnecessary work.

Declarative setup is based on database structure declarations, and is used in projects such as Doctrine. Schema files declare what the database structure should be, and the application determines the differences between the current table structure and what it should be. These differences can be represented with atomic SQL operations.

The application prioritizes the declarative schema and executes the declarative install schemas before the data and schema patches.

The following example, extracted from the Catalog/etc/db_schema.xml file, defines the catalog_product_entity_datetime table:

<table name="catalog_product_entity_datetime" resource="default" engine="innodb"
           comment="Catalog Product Datetime Attribute Backend Table">
    <column xsi:type="int" name="value_id" unsigned="false" nullable="false" identity="true" comment="Value ID"/>
    <column xsi:type="smallint" name="attribute_id" unsigned="true" nullable="false" identity="false" default="0" comment="Attribute ID"/>
    <column xsi:type="smallint" name="store_id" unsigned="true" nullable="false" identity="false" default="0" comment="Store ID"/>
    <column xsi:type="int" name="entity_id" unsigned="true" nullable="false" identity="false" default="0" comment="Entity ID"/>
    <column xsi:type="datetime" name="value" on_update="false" nullable="true" comment="Value"/>
    <constraint xsi:type="primary" referenceId="PRIMARY">
        <column name="value_id"/>
    </constraint>
    <constraint xsi:type="foreign" referenceId="CAT_PRD_ENTT_DTIME_ATTR_ID_EAV_ATTR_ATTR_ID" table="catalog_product_entity_datetime" column="attribute_id" referenceTable="eav_attribute" referenceColumn="attribute_id" onDelete="CASCADE"/>
    <constraint xsi:type="foreign" referenceId="CAT_PRD_ENTT_DTIME_ENTT_ID_CAT_PRD_ENTT_ENTT_ID" table="catalog_product_entity_datetime" column="entity_id" referenceTable="catalog_product_entity" referenceColumn="entity_id" onDelete="CASCADE"/>
    <constraint xsi:type="foreign" referenceId="CATALOG_PRODUCT_ENTITY_DATETIME_STORE_ID_STORE_STORE_ID" table="catalog_product_entity_datetime" column="store_id" referenceTable="store" referenceColumn="store_id" onDelete="CASCADE"/>
    <constraint xsi:type="unique" referenceId="CATALOG_PRODUCT_ENTITY_DATETIME_ENTITY_ID_ATTRIBUTE_ID_STORE_ID">
        <column name="entity_id"/>
        <column name="attribute_id"/>
        <column name="store_id"/>
    </constraint>
    <index referenceId="CATALOG_PRODUCT_ENTITY_DATETIME_ATTRIBUTE_ID" indexType="btree">
        <column name="attribute_id"/>
    </index>
    <index referenceId="CATALOG_PRODUCT_ENTITY_DATETIME_STORE_ID" indexType="btree">
        <column name="store_id"/>
    </index>
</table>

db_schema structure

The <Module_Vendor>/<Module_Name>/etc/db_schema.xml file declares a module's database structure.

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If you have enabled URN highlighting, you can use the PhpStorm autocomplete feature after choosing a node's xsi:type. This will also allow you to view which attributes are available on each line of your db_schema.xml file

Top-level node

The schema node defines the location of the schema.xsd file.

<schema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="urn:magento:framework:Setup/Declaration/Schema/etc/schema.xsd">

table node

Each db_schema.xml file should contain one or more table nodes. Each table node represents a table in the database. A table node can contain the following attributes:

Attribute
Description
name
The name of the table
engine
SQL engine. This value must be innodb or memory.
resource
The database shard on which to install the table. This value must be a database resource. The defaults for Commerce are default, checkout, and sales.
comment
Table comment.
onCreate
This is a DML trigger that allows you to move data from an existing table to a newly created table. This trigger works only when a table is created.

A table node can contain three types of subnodes:

column subnode

The column subnode defines a column in a table. Each column requires its own declaration.

A column can have the following attributes:

Attribute
Description
xsi:type
Specifies the column type. See valid values below.
default
Initializes the column with the specified default value. The default value should have the same datatype defined in xsi:type.
disabled
Disables or deletes the declared table, column, constraint, or index.
identity
Indicates whether a column is auto incremented.
length
Specifies the length of a column. Can be used for char, varchar, and varbinary types.
nullable
Indicates whether column can be nullable.
onCreate
This is a DDL trigger that allows you to move data from an existing column to a newly created column. This trigger works only when a column is created.
padding
The size of an integer column.
precision
The number of allowed digits in a real data type.
scale
The number of digits after the decimal in a real data type.
unsigned
For numeric data types, specifies whether the column can contain positive and negative values or only positive values.

Valid xsi:type values:

For more information about each type, refer to the annotations in the corresponding XSD file.

Example:

<column xsi:type="int" name="entity_id" unsigned="true" nullable="false" identity="true" comment="Credit ID"/>

constraint subnode

The constraint subnode always contains the following attributes:

Attribute
Description
type
One of primary, unique, or foreign
referenceId
A custom identifier that is used only for relation mapping in the scope of db_schema.xml files. The real entity in the database has a system-generated name. The most convenient way to set the value of this attribute is to use the value that is written in the module's db_schema_whitelist.json file when you run the generate-whitelist command.

The primary and unique constraints are called "internal" constraints, because they can be applied only to the scope of the table where they are created. Internal constraints define one or more column subnodes. Each subnode defines a constrained column.

The following example shows the format of an internal constraint.

<constraint xsi:type="primary" referenceId="PRIMARY">
    <column name="entity_id"/>
</constraint>

The foreign constraint is similar to foreign keys in SQL. This type of constraint connects two tables with each other. The following attributes define a foreign constraint:

Attribute
Description
table
The name of the current table
column
A column in the current table that refers to a specific column in another table
referenceTable
The table being referenced
referenceColumn
A column in the referenceTable
onDelete
Foreign key trigger. The value must be CASCADE, SET NULL, or NO ACTION
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To keep entity identifiers as immutable values, the declarative schema does not support ON UPDATE action for constraint.

Example:

<constraint xsi:type="foreign" referenceId="COMPANY_CREDIT_COMPANY_ID_COMPANY_ENTITY_ID" table="company_credit" column="company_id" referenceTable="company" referenceColumn="entity_id" onDelete="CASCADE"/>

index subnode

The index subnode has the same structure as internal constraints but contains different logic. While constraints are used for defining limitations, indexes are used for speeding up DQL operations. The following attributes define an index:

Attribute
Description
referenceId
A custom identifier that is used only for relation mapping in the scope of db_schema.xml files. The real entity in the database has a system-generated name. The most convenient way to set the value of this attribute is to use the value that is written in the module's db_schema_whitelist.json file when you run the generate-whitelist command.
indexType
The value must be btree, fulltext, or hash

Example:

<index referenceId="NEWSLETTER_SUBSCRIBER_CUSTOMER_ID" indexType="btree">
    <column name="customer_id"/>
</index>

Perform common database operations

This section shows how to perform common database operations using declarative schema. The screen captures use git diff to illustrate how to perform these tasks.

Create a table

The following example creates the declarative_table table with four columns. The id_column column is the primary key.

<schema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                 xsi:noNamespaceSchemaLocation="urn:magento:framework:Setup/Declaration/Schema/etc/schema.xsd">
+    <table name="declarative_table">
+        <column xsi:type="int" name="id_column" unsigned="true" nullable="false" comment="Entity Id"/>
+        <column xsi:type="int" name="severity" unsigned="true" nullable="false" comment="Severity code"/>
+        <column xsi:type="varchar" name="title" nullable="false" length="255" comment="Title"/>
+        <column xsi:type="timestamp" name="time_occurred" comment="Time of event"/>
+        <constraint xsi:type="primary" referenceId="PRIMARY">
+            <column name="id_column"/>
+        </constraint>
+    </table>
</schema>

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When creating a new table, remember to generate the db_schema_whitelist.json file.

Drop a table

In the following example, the declarative_table table was completely removed from the db_schema.xml file.

<schema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                 xsi:noNamespaceSchemaLocation="urn:magento:framework:Setup/Declaration/Schema/etc/schema.xsd">
-    <table name="declarative_table">
-        <column xsi:type="int" name="id_column" unsigned="true" nullable="false" comment="Entity Id"/>
-        <column xsi:type="int" name="severity" unsigned="true" nullable="false" comment="Severity code"/>
-        <column xsi:type="varchar" name="title" nullable="false" length="255" comment="Title"/>
-        <column xsi:type="timestamp" name="time_occurred" comment="Time of event"/>
-        <constraint xsi:type="primary" referenceId="PRIMARY">
-            <column name="id_column"/>
-        </constraint>
-    </table>
</schema>

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When dropping a table, do not remove it from the db_schema_whitelist.json file, otherwise it will not be dropped.

Rename a table

Table renaming is supported. The declarative schema will create a new table with the new name and drop the table with the old name. Renaming a table via RENAME TABLE is NOT supported. To migrate data from another table, specify the onCreate attribute on the table declaration, and add specify the source table name:

onCreate="migrateDataFromAnotherTable(catalog_category_entity)"

Please note that migrating data from another table and renaming columns at the same time is not supported.

This declarative process of renaming a table is not fast. If you need to migrate lots of data quickly you can create a CSV table dump using the --safe-mode=1 and add the data manually by using data/recurring patches.

<schema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                 xsi:noNamespaceSchemaLocation="urn:magento:framework:Setup/Declaration/Schema/etc/schema.xsd">
+    <table name="new_declarative_table" onCreate="migrateDataFromAnotherTable(declarative_table)">
-    <table name="declarative_table">
        <column xsi:type="int" name="id_column" unsigned="true" nullable="false" comment="Entity Id"/>
        <column xsi:type="int" name="severity" unsigned="true" nullable="false" comment="Severity code"/>
        <column xsi:type="varchar" name="title" nullable="false" length="255" comment="Title"/>
        <column xsi:type="timestamp" name="time_occurred" comment="Time of event"/>
        <constraint xsi:type="primary" referenceId="PRIMARY">
            <column name="id_column"/>
        </constraint>
    </table>
</schema>

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When renaming a table, remember to regenerate the db_schema_whitelist.json file so it contains the new name in addition to the old one.

Add a column to table

The following example adds the date_closed column.

<schema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                 xsi:noNamespaceSchemaLocation="urn:magento:framework:Setup/Declaration/Schema/etc/schema.xsd">
    <table name="declarative_table">
        <column xsi:type="int" name="id_column" unsigned="true" nullable="false" comment="Entity Id"/>
        <column xsi:type="int" name="severity" unsigned="true" nullable="false" comment="Severity code"/>
        <column xsi:type="varchar" name="title" nullable="false" length="255" comment="Title"/>
        <column xsi:type="timestamp" name="time_occurred" comment="Time of event"/>
+       <column xsi:type="timestamp" name="date_closed" comment="Time of event"/>
        <constraint xsi:type="primary" referenceId="PRIMARY">
            <column name="id_column"/>
        </constraint>
    </table>
</schema>

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When adding a new column into table, remember to generate the db_schema_whitelist.json file.

Drop a column from a table

The following example removes the date_closed column by deleting its column node. To drop a column declared in another module, redeclare it with the disabled attribute set to true.

<schema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                 xsi:noNamespaceSchemaLocation="urn:magento:framework:Setup/Declaration/Schema/etc/schema.xsd">
    <table name="declarative_table">
        <column xsi:type="int" name="id_column" unsigned="true" nullable="false" comment="Entity Id"/>
        <column xsi:type="int" name="severity" unsigned="true" nullable="false" comment="Severity code"/>
        <column xsi:type="varchar" name="title" nullable="false" length="255" comment="Title"/>
        <column xsi:type="timestamp" name="time_occurred" comment="Time of event"/>
-       <column xsi:type="timestamp" name="date_closed" comment="Time of event"/>
        <constraint xsi:type="primary" referenceId="PRIMARY">
            <column name="id_column"/>
        </constraint>
    </table>
</schema>

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It is possible to drop a column only if it exists in the db_schema_whitelist.json file.

Change the column type

The following example changes the type of the title column from varchar to text.

<schema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                 xsi:noNamespaceSchemaLocation="urn:magento:framework:Setup/Declaration/Schema/etc/schema.xsd">
    <table name="declarative_table">
        <column xsi:type="int" name="id_column" unsigned="true" nullable="false" comment="Entity Id"/>
        <column xsi:type="int" name="severity" unsigned="true" nullable="false" comment="Severity code"/>
-       <column xsi:type="varchar" name="title" nullable="false" length="255" comment="Title"/>
+       <column xsi:type="text" name="title" nullable="false" comment="Title"/>
        <column xsi:type="timestamp" name="time_occurred" comment="Time of event"/>
        <constraint xsi:type="primary" referenceId="PRIMARY">
            <column name="id_column"/>
        </constraint>
    </table>
</schema>

Rename a column

To rename a column, delete the original column declaration and create a new one. In the new column declaration, use the onCreate attribute to specify which column to migrate data from. Use the following construction to migrate data from the same table.

onCreate="migrateDataFrom(entity_id)"

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When renaming a column, remember to regenerate the db_schema_whitelist.json file so it contains the new name in addition to the old one.

Add an index

The following example adds the INDEX_SEVERITY index to the declarative_table table.

<schema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                 xsi:noNamespaceSchemaLocation="urn:magento:framework:Setup/Declaration/Schema/etc/schema.xsd">
    <table name="declarative_table">
        <column xsi:type="int" name="id_column" unsigned="true" nullable="false" comment="Entity Id"/>
        <column xsi:type="int" name="severity" unsigned="true" nullable="false" comment="Severity code"/>
        <column xsi:type="text" name="title" nullable="false" length="255" comment="Title"/>
        <column xsi:type="timestamp" name="time_occurred" comment="Time of event"/>
        <constraint xsi:type="primary" referenceId="PRIMARY">
            <column name="id_column"/>
        </constraint>
+       <index referenceId="INDEX_SEVERITY" indexType="btree">
+           <column name="severity"/>
+       </index>
    </table>
</schema>

Create a foreign key

In the following example, the selected constraint node defines the characteristics of the FL_ALLOWED_SEVERITIES foreign key.

<schema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                 xsi:noNamespaceSchemaLocation="urn:magento:framework:Setup/Declaration/Schema/etc/schema.xsd">
    <table name="declarative_table">
        <column xsi:type="int" name="id_column" unsigned="true" nullable="false" comment="Entity Id"/>
        <column xsi:type="int" name="severity" unsigned="true" nullable="false" comment="Severity code"/>
        <column xsi:type="varchar" name="title" nullable="false" length="255" comment="Title"/>
        <column xsi:type="timestamp" name="time_occurred" comment="Time of event"/>
        <constraint xsi:type="primary" referenceId="PRIMARY">
            <column name="id_column"/>
        </constraint>
+       <constraint xsi:type="foreign" referenceId="FL_ALLOWED_SEVERITIES" table="declarative_table"
+               column="severity" referenceTable="severities" referenceColumn="severity_identifier"
+               onDelete="CASCADE"/>
    </table>
</schema>

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Foreign keys can only be added to tables when both tables were created using a declarative schema (db_schema.xml).

Drop a foreign key

The following example removes the FL_ALLOWED_SEVERITIES foreign key by deleting its constraint node. To drop a constraint declared in another module, redeclare it with the disabled attribute set to true.

<schema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                 xsi:noNamespaceSchemaLocation="urn:magento:framework:Setup/Declaration/Schema/etc/schema.xsd">
    <table name="declarative_table">
        <column xsi:type="int" name="id_column" unsigned="true" nullable="false" comment="Entity Id"/>
        <column xsi:type="int" name="severity" unsigned="true" nullable="false" comment="Severity code"/>
        <column xsi:type="varchar" name="title" nullable="false" length="255" comment="Title"/>
        <column xsi:type="timestamp" name="time_occurred" comment="Time of event"/>
        <constraint xsi:type="primary" referenceId="PRIMARY">
            <column name="id_column"/>
        </constraint>
-       <constraint xsi:type="foreign" referenceId="FL_ALLOWED_SEVERITIES" table="declarative_table"
-               column="severity" referenceTable="severities" referenceColumn="severity_identifier"
-               onDelete="CASCADE"/>
    </table>
</schema>

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It is possible to drop a foreign key only if it exists in the db_schema_whitelist.json file.

Recreate a foreign key

In this example, Module A defines a new table with primary key id_column. Module B declares its own schema, in which it creates a new column (new_id_column) and changes the primary index to this column. Module B disables the original primary key and sets a new primary key with a referenceId value that is different from PRIMARY. Although this value is different, the real name of the primary key in the database remains PRIMARY.

Module A declaration:

<schema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                 xsi:noNamespaceSchemaLocation="urn:magento:framework:Setup/Declaration/Schema/etc/schema.xsd">
    <table name="declarative_table">
        <column xsi:type="int" name="id_column" unsigned="true" nullable="false" comment="Entity Id"/>
        <constraint xsi:type="primary" referenceId="PRIMARY">
            <column name="id_column"/>
        </constraint>
    </table>
</schema>

Module B declaration:

<schema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:framework:Setup/Declaration/Schema/etc/schema.xsd">
    <table name="declarative_table">
        <column xsi:type="int" name="new_id_column" unsigned="true" nullable="false"
                comment="New Entity Id"/>
        <constraint xsi:type="primary" referenceId="PRIMARY" disabled="true"/>
        <constraint xsi:type="primary" referenceId="NEW_PRIMARY">
            <column name="new_id_column"/>
        </constraint>
    </table>
</schema>

Other tasks

Disable a module

When a module is disabled in app/etc/config.php, its database schema configuration is no longer read on upgrade or install. As a result, subsequent system upgrades rebuild the database schema without the module's tables, columns, or other elements. Please note that the db_schema_whitelist.json file of disabled modules is still read during upgrades of installs, so the declarative schema system can perform the necessary operations. Practically, this means that if you disable a module which uses declarative schema and run bin/magento setup:upgrade, its database tables will be dropped (see more details and discussion at https://github.com/magento/magento2/issues/24926). Please consider using setup:upgrade --safe-mode=1 in order to create a database backup after disabling a module and then eventually setup:upgrade --data-restore=1 if you enable the module back and wish to restore from that backup.