The XML mapping driver enables you to provide the ORM metadata in form of XML documents.

The XML driver is backed by an XML Schema document that describes the structure of a mapping document. The most recent version of the XML Schema document is available online at [http://www.doctrine-project.org/schemas/orm/doctrine-mapping.xsd](http://www.doctrine-project.org/schemas/orm/doctrine-mapping.xsd). In order to point to the latest version of the document of a particular stable release branch, just append the release number, i.e.: doctrine-mapping-2.0.xsd  The most convenient way to work with XML mapping files is to use an IDE/editor that can provide code-completion based on such an XML Schema document. The following is an outline of a XML mapping document with the proper xmlns/xsi setup for the latest code in trunk.

    [xml]
    <doctrine-mapping xmlns="http://doctrine-project.org/schemas/orm/doctrine-mapping"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://doctrine-project.org/schemas/orm/doctrine-mapping
                        http://doctrine-project.org/schemas/orm/doctrine-mapping.xsd">
    
        ...
    
    </doctrine-mapping>
    
The XML mapping document of a class is loaded on-demand the first time it is requested and subsequently stored in the metadata cache. In order to work, this requires certain conventions:

 * Each entity/mapped superclass must get its own dedicated XML mapping document.
 * The name of the mapping document must consist of the fully qualified name of the class, where namespace
   separators are replaced by dots (.). For example an Entity with the fully qualified class-name "MyProject\Entities\User"
   would require a mapping file "MyProject.Entities.User.dcm.xml" unless the extension is changed.
 * All mapping documents should get the extension ".dcm.xml" to identify it as a Doctrine mapping file. This is more of
   a convention and you are not forced to do this. You can change the file extension easily enough.
 
-

    <?php
    $driver->setFileExtension('.xml');

It is recommended to put all XML mapping documents in a single folder but you can spread the documents over several folders if you want to. In order to tell the XmlDriver where to look for your mapping documents, supply an array of paths as the first argument of the constructor, like this:

    <?php
    $config = new \Doctrine\ORM\Configuration();
    $driver = new \Doctrine\ORM\Mapping\Driver\XmlDriver(array('/path/to/files1', '/path/to/files2'));
    $config->setMetadataDriverImpl($driver);


## Example

As a quick start, here is a small example document that makes use of several common elements:

    [xml]
    // Doctrine.Tests.ORM.Mapping.User.dcm.xml
    <?xml version="1.0" encoding="UTF-8"?>
    <doctrine-mapping xmlns="http://doctrine-project.org/schemas/orm/doctrine-mapping"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://doctrine-project.org/schemas/orm/doctrine-mapping
                              http://www.doctrine-project.org/schemas/orm/doctrine-mapping.xsd">

        <entity name="Doctrine\Tests\ORM\Mapping\User" table="cms_users">

            <indexes>
                <index name="name_idx" columns="name"/>
                <index columns="user_email"/>
            </indexes>

            <unique-constraints>
                <unique-constraint columns="name,user_email" name="search_idx" />
            </unique-constraints>

            <lifecycle-callbacks>
                <lifecycle-callback type="prePersist" method="doStuffOnPrePersist"/>
                <lifecycle-callback type="prePersist" method="doOtherStuffOnPrePersistToo"/>
                <lifecycle-callback type="postPersist" method="doStuffOnPostPersist"/>
            </lifecycle-callbacks>

            <id name="id" type="integer" column="id">
                <generator strategy="AUTO"/>
                <sequence-generator sequence-name="tablename_seq" allocation-size="100" initial-value="1" />
            </id>

            <field name="name" column="name" type="string" length="50" nullable="true" unique="true" />
            <field name="email" column="user_email" type="string" column-definition="CHAR(32) NOT NULL" />

            <one-to-one field="address" target-entity="Address" inversed-by="user">
                <cascade><cascade-remove /></cascade>
                <join-column name="address_id" referenced-column-name="id" on-delete="CASCADE" on-update="CASCADE"/>
            </one-to-one>

            <one-to-many field="phonenumbers" target-entity="Phonenumber" mapped-by="user">
                <cascade>
                    <cascade-persist/>
                </cascade>
                <order-by>
                    <order-by-field name="number" direction="ASC" />
                </order-by>
            </one-to-many>

            <many-to-many field="groups" target-entity="Group">
                <cascade>
                    <cascade-all/>
                </cascade>
                <join-table name="cms_users_groups">
                    <join-columns>
                        <join-column name="user_id" referenced-column-name="id" nullable="false" unique="false" />
                    </join-columns>
                    <inverse-join-columns>
                        <join-column name="group_id" referenced-column-name="id" column-definition="INT NULL" />
                    </inverse-join-columns>
                </join-table>
            </many-to-many>

        </entity>

    </doctrine-mapping>

 Be aware that class-names specified in the XML files should be fully qualified.

## XML-Element Reference

The XML-Element reference explains all the tags and attributes that the Doctrine Mapping XSD Schema defines.
You should read the Basic-, Association- and Inheritance Mapping chapters to understand what each of this
definitions means in detail.

### Defining an Entity

Each XML Mapping File contains the definition of one entity, specified as the `<entity />` element
as a direct child of the `<doctrine-mapping />` element:

    [xml]
    <doctrine-mapping>
        <entity name="MyProject\User" table="cms_users" repository-class="MyProject\UserRepository">
            <!-- definition here -->
        </entity>
    </doctrine-mapping>

Required attributes:

* name - The fully qualified class-name of the entity.

Optional attributes:

* table - The Table-Name to be used for this entity. Otherwise the Unqualified Class-Name is used by default.
* repository-class - The fully qualified class-name of an alternative `Doctrine\ORM\EntityRepository` implementation to be used with this entity.
* inheritance-type - The type of inheritance, defaults to none. A more detailed description follows in the *Defining Inheritance Mappings* section.

### Defining Fields

Each entity class can contain zero to infinite fields that are managed by Doctrine. You can define
them using the `<field />` element as a children to the `<entity />` element. The field element is only
used for primitive types that are not the ID of the entity. For the ID mapping you have to use the `<id />` element.

    [xml]
    <entity name="MyProject\User">

        <field name="name" type="string" length="50" />
        <field name="username" type="string" unique="true" />
        <field name="age" type="integer" nullable="true" />
        <field name="isActive" column="is_active" type="boolean" />
        <field name="weight" type="decimal" scale="5" precision="2" />
    </entity>

Required attributes:

* name - The name of the Property/Field on the given Entity PHP class.

Optional attributes:

* type - The `Doctrine\DBAL\Types\Type` name, defaults to "string"
* column - Name of the column in the database, defaults to the field name.
* length - The length of the given type, for use with strings only.
* unique - Should this field contain a unique value across the table? Defaults to false.
* nullable - Should this field allow NULL as a value? Defaults to false.
* version - Should this field be used for optimistic locking? Only works on fields with type integer or datetime.
* scale - Scale of a decimal type.
* precision - Precision of a decimal type.
* column-definition - Optional alternative SQL representation for this column. This definition begin after the
  field-name and has to specify the complete column definition. Using this feature will turn this field dirty
  for Schema-Tool update commands at all times.

### Defining Identity and Generator Strategies

An entity has to have at least one `<id />` element. For composite keys you can specify more than one id-element,
however surrogate keys are recommended for use with Doctrine 2. The Id field allows to define properties of
the identifier and allows a subset of the `<field />` element attributes:

    [xml]
    <entity name="MyProject\User">
        <id name="id" type="integer" column="user_id" />
    </entity>

Required attributes:

* name - The name of the Property/Field on the given Entity PHP class.
* type - The `Doctrine\DBAL\Types\Type` name, preferably "string" or "integer".

Optional attributes:

* column - Name of the column in the database, defaults to the field name.

Using the simplified definition above Doctrine will use no identifier strategy for this entity. That means
you have to manually set the identifier before calling `EntityManager#persist($entity)`. This is the
so called `ASSIGNED` strategy.

If you want to switch the identifier generation strategy you have to nest a `<generator />` element inside
the id-element. This of course only works for surrogate keys. For composite keys you always have to use
the `ASSIGNED` strategy.

    [xml]
    <entity name="MyProject\User">
        <id name="id" type="integer" column="user_id">
            <generator strategy="AUTO" />
        </id>
    </entity>

The following values are allowed for the `<generator />` strategy attribute:

* AUTO - Automatic detection of the identifier strategy based on the preferred solution of the database vendor.
* IDENTITY - Use of a IDENTIFY strategy such as Auto-Increment IDs available to Doctrine AFTER the INSERT statement has been executed.
* SEQUENCE - Use of a database sequence to retrieve the entity-ids. This is possible before the INSERT statement is executed.

If you are using the SEQUENCE strategy you can define an additional element to describe the sequence:

    [xml]
    <entity name="MyProject\User">
        <id name="id" type="integer" column="user_id">
            <generator strategy="SEQUENCE" />
            <sequence-generator sequence-name="user_seq" allocation-size="5" initial-value="1" />
        </id>
    </entity>

Required attributes for `<sequence-generator />`:

* sequence-name - The name of the sequence

Optional attributes for `<sequence-generator />`:

* allocation-size - By how much steps should the sequence be incremented when a value is retrieved. Defaults to 1
* initial-value - What should the initial value of the sequence be.

> **NOTE**
>
> If you want to implement a cross-vendor compatible application you have to specify <generator strategy="AUTO" /> and
> additionally define the <sequence-generator /> element, if Doctrine chooses the sequence strategy for a platform.

### Defining a Mapped Superclass

Sometimes you want to define a class that multiple entities inherit from, which itself is not an entity however.
The chapter on *Inheritance Mapping* describes a Mapped Superclass in detail. You can define it in XML using
the `<mapped-superclass />` tag.

    [xml]
    <doctrine-mapping>
        <mapped-superclass name="MyProject\BaseClass">
            <field name="created" type="datetime" />
            <field name="updated" type="datetime" />
        </mapped-superclass>
    </doctrine-mapping>

Required attributes:

* name - Class name of the mapped superclass.

You can nest any number of `<field />` and unidirectional `<many-to-one />` or `<one-to-one />` associations inside
a mapped superclass.

### Defining Inheritance Mappings

There are currently two inheritance persistence strategies that you can choose from when defining entities that
inherit from each other. Single Table inheritance saves the fields of the complete inheritance hierarchy in a single table,
joined table inheritance creates a table for each entity combining the fields using join conditions.

You can specify the inheritance type in the `<entity />` element and then use the `<discriminator-column />` and
`<discriminator-mapping />` attributes.

    [xml]
    <entity name="MyProject\Animal" inheritance-type="JOINED">
        <discriminator-column name="discr" type="string" />
        <discriminator-map>
            <discriminator-mapping value="cat" class="MyProject\Cat" />
            <discriminator-mapping value="dog" class="MyProject\Dog" />
            <discriminator-mapping value="mouse" class="MyProject\Mouse" />
        </discriminator-map>
    </entity>

The allowed values for inheritance-type attribute are `JOINED` or `SINGLE_TABLE`.

> **NOTE**
>
> All inheritance related definitions have to be defined on the root entity of the hierarchy.

### Defining Lifecycle Callbacks

You can define the lifecycle callback methods on your entities using the `<lifecycle-callbacks />` element:

    [xml]
    <entity name="Doctrine\Tests\ORM\Mapping\User" table="cms_users">

        <lifecycle-callbacks>
            <lifecycle-callback type="prePersist" method="onPrePersist" />
        </lifecycle-callbacks>
    </entity>

### Defining One-To-One Relations

You can define One-To-One Relations/Associations using the `<one-to-one />` element. The required
and optional attributes depend on the associations being on the inverse or owning side.

For the inverse side the mapping is as simple as:

    [xml]
    <entity class="MyProject\User">
        <one-to-one field="address" target-entity="Address" mapped-by="user" />
    </entity>

Required attributes for inverse One-To-One:

* field - Name of the property/field on the entity's PHP class.
* target-entity - Name of the entity associated entity class. If this is not qualified the namespace of the current class is prepended. *IMPORTANT:* No leading backslash!
* mapped-by - Name of the field on the owning side (here Address entity) that contains the owning side association.

For the owning side this mapping would look like:

    [xml]
    <entity class="MyProject\Address">
        <one-to-one field="user" target-entity="User" inversed-by="address" />
    </entity>

Required attributes for owning One-to-One:

* field - Name of the property/field on the entity's PHP class.
* target-entity - Name of the entity associated entity class. If this is not qualified the namespace of the current class is prepended. *IMPORTANT:* No leading backslash!

Optional attributes for owning One-to-One:

* inversed-by - If the association is bidirectional the inversed-by attribute has to be specified with the name of the field on the inverse entity that contains the back-reference.
* orphan-removal - If true, the inverse side entity is always deleted when the owning side entity is. Defaults to false.
* fetch - Either LAZY or FETCH, defaults to LAZY. This attribute makes only sense on the owning side, the inverse side *ALWAYS* has to use the `FETCH` strategy.

The definition for the owning side relies on a bunch of mapping defaults for the join column names.
Without the nested `<join-column />` element Doctrine assumes to foreign key to be called `user_id` on the Address
Entities table. This is because the `MyProject\Address` entity is the owning side of this association, which means
it contains the foreign key.

The completed explicitly defined mapping is:

    [xml]
    <entity class="MyProject\Address">
        <one-to-one field="user" target-entity="User" inversed-by="address">
            <join-column name="user_id" referenced-column-name="id" />
        </one-to-one>
    </entity>

### Defining Many-To-One Associations

The many-to-one association is *ALWAYS* the owning side of any bidirectional association. This simplifies the mapping
compared to the one-to-one case. The minimal mapping for this association looks like:

    [xml]
    <entity class="MyProject\Article">
        <many-to-one field="author" target-entity="User" />
    </entity>

Required attributes:

* field - Name of the property/field on the entity's PHP class.
* target-entity - Name of the entity associated entity class. If this is not qualified the namespace of the current class is prepended. *IMPORTANT:* No leading backslash!

Optional attributes:

* inversed-by - If the association is bidirectional the inversed-by attribute has to be specified with the name of the field on the inverse entity that contains the back-reference.
* orphan-removal - If true the entity on the inverse side is always deleted when the owning side entity is and it is not connected to any other owning side entity anymore. Defaults to false.
* fetch - Either LAZY or FETCH, defaults to LAZY.

This definition relies on a bunch of mapping defaults with regards to the naming of the join-column/foreign key. The
explicitly defined mapping includes a `<join-column />` tag nested inside the many-to-one association tag:

    [xml]
    <entity class="MyProject\Article">
        <many-to-one field="author" target-entity="User">
            <join-column name="author_id" referenced-column-name="id" />
        </many-to-one>
    </entity>

The join-column attribute `name` specifies the column name of the foreign key and
the `referenced-column-name` attribute specifies the name of the primary key column
on the User entity.

### Defining One-To-Many Associations

The one-to-many association is *ALWAYS* the inverse side of any association. There exists no such thing as a
uni-directional one-to-many association, which means this association only ever exists for bi-directional associations.

    [xml]
    <entity class="MyProject\User">
        <one-to-many field="phonenumbers" target-entity="Phonenumber" mapped-by="user" />
    </entity>

Required attributes:

* field - Name of the property/field on the entity's PHP class.
* target-entity - Name of the entity associated entity class. If this is not qualified the namespace of the current class is prepended. *IMPORTANT:* No leading backslash!
* mapped-by - Name of the field on the owning side (here Phonenumber entity) that contains the owning side association.

Optional attributes:

* fetch - Either LAZY or FETCH, defaults to LAZY.

### Defining Many-To-Many Associations

From all the associations the many-to-many has the most complex definition. When you rely on the mapping defaults
you can omit many definitions and rely on their implicit values.

    [xml]
    <entity class="MyProject\User">
        <many-to-many field="groups" target-entity="Group" />
    </entity>

Required attributes:

* field - Name of the property/field on the entity's PHP class.
* target-entity - Name of the entity associated entity class. If this is not qualified the namespace of the current class is prepended. *IMPORTANT:* No leading backslash!

Optional attributes:

* mapped-by - Name of the field on the owning side that contains the owning side association if the defined many-to-many association is on the inverse side.
* inversed-by - If the association is bidirectional the inversed-by attribute has to be specified with the name of the field on the inverse entity that contains the back-reference.
* fetch - Either LAZY or FETCH, defaults to LAZY.

The mapping defaults would lead to a join-table with the name "User_Group" being created that contains two columns
"user_id" and "group_id". The explicit definition of this mapping would be:

    [xml]
    <entity class="MyProject\User">
        <many-to-many field="groups" target-entity="Group">
            <join-table name="cms_users_groups">
                <join-columns>
                    <join-column name="user_id" referenced-column-name="id"/>
                </join-columns>
                <inverse-join-columns>
                    <join-column name="group_id" referenced-column-name="id"/>
                </inverse-join-columns>
            </join-table>
        </many-to-many>
    </entity>

Here both the `<join-columns>` and `<inverse-join-columns>` tags are necessary to tell Doctrine for which side the
specified join-columns apply. These are nested inside a `<join-table />` attribute which allows to specify
the table name of the many-to-many join-table.

### Cascade Element

Doctrine allows cascading of several UnitOfWork operations to related entities. You can specify the cascade
operations in the `<cascade />` element inside any of the association mapping tags.

    [xml]
    <entity class="MyProject\User">
        <many-to-many field="groups" target-entity="Group">
            <cascade>
                <cascade-all/>
            </cascade>
        </many-to-many>
    </entity>

Besides `<cascade-all />` the following operations can be specified by their respective tags:

* `<cascade-persist />`
* `<cascade-merge />`
* `<cascade-remove />`
* `<cascade-refresh />`

### Join Column Element

In any explicitly defined association mapping you will need the `<join-column />` tag. It defines how the
foreign key and primary key names are called that are used for joining two entities.

Required attributes:

* name - The column name of the foreign key.
* referenced-column-name - The column name of the associated entities primary key

Optional attributes:

* unique - If the join column should contain a UNIQUE constraint. This makes sense for Many-To-Many join-columns only to simulate a one-to-many unidirectional using a join-table.
* nullable - should the join column be nullable, defaults to true.
* on-delete - Foreign Key Cascade action to perform when entity is deleted, defaults to NO ACTION/RESTRICT but can be set to "CASCADE".

### Defining Order of To-Many Associations

You can require one-to-many or many-to-many associations to be retrieved using an additional `ORDER BY`.

    [xml]
    <entity class="MyProject\User">
        <many-to-many field="groups" target-entity="Group">
            <order-by>
                <order-by-field name="name" direction="ASC" />
            </order-by>
        </many-to-many>
    </entity>

### Defining Indexes or Unique Constraints

To define additional indexes or unique constraints on the entities table you can use the
`<indexes />` and `<unique-constraints />` elements:

    [xml]
    <entity name="Doctrine\Tests\ORM\Mapping\User" table="cms_users">

        <indexes>
            <index name="name_idx" columns="name"/>
            <index columns="user_email"/>
        </indexes>

        <unique-constraints>
            <unique-constraint columns="name,user_email" name="search_idx" />
        </unique-constraints>
    </entity>

You have to specify the column and not the entity-class field names in the index and unique-constraint
definitions.