This release fixes an issue related to a long standing issue with how

PHP handles loading of external XML entities (https://bugs.php.net/bug.php?id=62577).

Total issues resolved: **2**

- [3788: DDC-3020: `simplexml_load_file()`: I/O warning: failed to load external in `XmlDriver`](doctrine#3788) thanks to @doctrinebot
- [6633: `XmlDriver`: Avoid PHP bug #62577 by avoiding `simplexml_load_file()`](doctrine#6633) thanks to @apapsch

This release fixes a couple regression introduced by

v2.5.7 and v2.5.8.

Specifically, `AbstractHydrator#hydrateAll()` was raising
`E_NOTICE` errors due to it not being registered with the
`EventManager`, yet trying to remove itself from the
registered listeners. [doctrine#6623](doctrine#6623)

In addition to that, having embeddable `final` classes
would cause errors being raised while trying to generate
proxies. The ORM will no longer attempt to generate proxies
for embeddables. [doctrine#6625](doctrine#6623)

Total issues resolved: **3**

- [6623: Ensure that `AbstractHydrator#hydrateAll()` detaches the hydrator from the event manager](doctrine#6623) thanks to @echo511
- [6625: Proxy generation for embedded/transient classes](doctrine#6625) thanks to @bendavies
- [6626: doctrine#6625 Skip proxy generation for embeddable classes](doctrine#6626) thanks to @issei-m

This release solves a bug introduced while backporting

[doctrine#6464](doctrine#6464)
and [doctrine#6475](doctrine#6475).
Specifically, a dangling undefined variable remained in the
code, causing some `SqlWalker` functionality to misbehave.
The undefined variable wasn't noticed due to it being placed
in an `empty()` expression.

Total issues resolved: **1**

- [6621: Fixed usage of undefined variable in `empty()` expression in `SqlWalker`](doctrine#6621) thanks to @Powerhamster

This release fixes a number of bugs detected in the current stable

release of the ORM.

This patch introduces compatibility with Doctrine DBAL 2.6.x. [doctrine#6580](doctrine#6580)

The most critical issue being fixed is a bug
in `Doctrine\ORM\PersistentCollection`, causing duplicate data
to be persisted when a collection is both marked as initialized
and dirty, and more entries are added to it via
the `Doctrine\Common\Collections\Collection#add()`
API. [doctrine#6613](doctrine#6613) [doctrine#6614](doctrine#6614)
[doctrine#6616](doctrine#6616)

The return value of `Doctrine\ORM\PersistentCollection#removeElement()`
was sometimes an `object` or `null, causing some applications
to crash when PHP is run within the context
of `declare(strict_types=1);` [doctrine#6550](doctrine#6550)

Memory leak issues with the hydrator process were fixed: the
hydrator object was never being garbage collected due to it
being registered with a `Doctrine\Common\EventManager` instance
to listen for the `Doctrine\ORM\Events::onClear` event. [doctrine#1515](doctrine#1515)

The `Doctrine\ORM\Tools\Pagination\CountOutputWalker` was producing
invalid SQL for queries containing a `GROUP BY` clause. [doctrine#6243](doctrine#6243)

The SQL generated for a DQL query containing a JTI (Joined Table
Inheritance) selection and a `WITH` clause applied to a `JOIN`
condition was invalid on PostgreSQL. [doctrine#6475](doctrine#6475)

The `Doctrine\ORM\Tools\Console\MetadataFilter` was not detecting
all metadata matching the filter regular expression. [doctrine#5715](doctrine#5715)

The `Doctrine\ORM\Tools\SchemaTool` was raising notices due to
invalid lookup for a discriminator column length, which may
not be defined in all mappings. [doctrine#5798](doctrine#5798)

Total issues resolved: **18**

- [1515: DDC-3146 Remove `onClear` event listener from abstract hydrator in cleanup function, otherwise causing hydrator GC to not kick in](doctrine#1515) thanks to @emiel-silverstreet
- [1541: Type annotation correction in `ResultSetMappingBuilder#addJoinedEntityFromClassMetadata()` `$relation` (should be `string`)](doctrine#1541) thanks to @aleeeftw
- [3925: DDC-3146: Hydrator memory leak when using iterator](doctrine#3925) thanks to @doctrinebot
- [4772: DDC-3914: doctrine#1515 DDC-3146 Remove event listener from abstract hydrator in cleanup function](doctrine#4772) thanks to @doctrinebot
- [5715: Fix `MetadataFilter` regression after doctrine#507 (doctrine#2815) not testing filters after first one](doctrine#5715) thanks to @guilliamxavier
- [5745: `PersistentCollection#removeElement()` returns `object` or `null` instead of boolean](doctrine#5745) thanks to @holtkamp
- [5798: Fix undefined index for discriminator column `length` attribute in `SchemaTool`](doctrine#5798) thanks to @sergeyfedotov
- [6243: Fix `CountOutputWalker` for queries containing a `GROUP BY` clause, which was producing invalid SQL](doctrine#6243) thanks to @enumag
- [6362: Undefined Property error in ObjectHydrator when using JOIN WITH](doctrine#6362) thanks to @SirWaddles
- [6367: Correct hydration of resultsets coming from DQL queries where the root of the selection is aliased and also the root of an inheritance](doctrine#6367) thanks to @SirWaddles
- [6381: Corrected `LoadClassMetadataEventArgs` `@method` annotations to reflect actual returned types](doctrine#6381) thanks to @ElisDN
- [6464: Query builder yields invalid SQL with JOINED inheritance type on PostgreSQL](doctrine#6464) thanks to @stesie
- [6475: Fix invalid sql generated for CTI JOINs when INNER JOIN'ing with a `WITH` clause](doctrine#6475) thanks to @stesie
- [6550: Fix return value of `PersistentCollection#removeElement()` for extra-lazy collections: should be `bool`](doctrine#6550) thanks to @alcaeus
- [6580: Allow DBAL 2.6 and common 2.8 to be installed](doctrine#6580) thanks to @Tobion
- [6613: There is the fail "UNIQUE constraint failed" with a LAZY collection](doctrine#6613) thanks to @Sysaninster
- [6614: `UNIQUE constraint failed` errors when manipulating a `LAZY` collection and calling `toArray()` on it](doctrine#6614) thanks to @Sysaninster
- [6616: doctrine#6613 doctrine#6614 correct handling of new elements added to an initialized (yet dirty) collection](doctrine#6616) thanks to @Ocramius

This release relaxes [`doctrine/common`](https://github.com/doctrine/…

…common) requirements

in order to allow installation of versions that support PHP 7.1 features in proxy class
generation. Please note that a similar requirement relaxation still needs to be applied to
[`doctrine/dbal`](https://github.com/doctrine/dbal) in order to allow installation of
the latest `doctrine/common` versions. [doctrine#6156](doctrine#6156)

This version also backports some fixes around the eviction of the second level cache entries
of inverse side associations in one-to-many - many-to-one mappings. [doctrine#6159](doctrine#6159)

Further fixes were applied in order to have child classes in inheritance mapping share the
same timestamp region when the second level cache is enabled. [doctrine#6028](doctrine#6028)

Also, `Doctrine\ORM\EntityManager#merge()` now triggers `Doctrine\ORM\Events::prePersist`
listeners with the merged entity state whenever an internal `Doctrine\ORM\UnitOfWork#persist()`
call is implied. [doctrine#6177](doctrine#6177).

Total issues resolved: **8**

- [5570: Fix PrePersist EventListener when using merge instead of persist](doctrine#5570)
- [6028: Make child entity share the timestamp region with parent class](doctrine#6028)
- [6110: Clear $this->collection even when empty, to reset keys](doctrine#6110)
- [6156: Allow doctrine/common 2.7](doctrine#6156)
- [6159: doctrine#5821 Backport doctrine#1551 - Fixed support for inverse side second level cache](doctrine#6159)
- [6174: Merging a new entity with PrePersist event make changes in callback not be considered](doctrine#6174)
- [6177: Fix doctrine#6174 doctrine#5570: merging new entities should also trigger prepersist lifecycle callbacks with merged entity data](doctrine#6177)
- [6178: Backport doctrine#6177 - fix doctrine#6174 doctrine#5570: merging new entities should also trigger prepersist lifecycle callbacks with the merged data](doctrine#6178)

This release includes a big amount of bugfixes.

Specifically, following issues were fixed:

 * Embeddable classes are now allowed in inheritance trees [4097](doctrine#4097)
 * Removed some object hash collisions caused by entity merging [1465](doctrine#1465)
 * Allowed usage of mathematical operators in DQL `HAVING` clauses [5598](doctrine#5598)
 * Fixed cloning of proxies with private properties at multiple inheritance levels [5755](doctrine#5755)
 * Entity insertions are correctly cleared when a specific entity is to be cleared [5849](doctrine#5849)
 * Corrected hydration of fetch-joins that use composite keys [5762](doctrine#5762)
 * Metadata exporters now only export the owning side metadata in a one-to-one relation [5858](doctrine#5858)
 * Corrected hydration of JTI entities when `NULL` is retrieved for a `simple_array` or `json_array` field [5989](doctrine#5989)
 * Correctly expire L2 cache query caches, based on entity region cache timestamp [6001](doctrine#6001)

Total issues resolved: **18**

- [1465: spl_object_hash conflict on Merge](doctrine#1465)
- [4097: DDC-3303: @Orm\Embedded does not work with extending classes](doctrine#4097)
- [4277: DDC-3467: Embeddable in inheritance must currently be protected](doctrine#4277)
- [5598: HAVING clause with variable and *, / math operators](doctrine#5598)
- [5599: Fix doctrine#5598 issue with /, * in DQL not translating query components properly](doctrine#5599)
- [5689: Avoid conflicts due to spl_object_hash](doctrine#5689)
- [5755: Error on entity clone for MappedSuperclass fields](doctrine#5755)
- [5762: fetch join using composite key on join entity fails to hydrate correctly](doctrine#5762)
- [5768: Fixes doctrine#5755 - Parent class fields are not cloned](doctrine#5768)
- [5776: add functional test and bug fix for issue doctrine#5762](doctrine#5776)
- [5849: `UnitOfWork#clear()` doesn't clear `entityInsertions` when `entityName` is passed](doctrine#5849)
- [5850: Clear `UnitOfWork#$entityInsertions` for specific entityName](doctrine#5850)
- [5858: Exporters should only inspect `joinColumns` for owning side in bi-directional OneToOne](doctrine#5858)
- [5867: Allow the usage of embedded objects on parent classes](doctrine#5867)
- [5975: Fix hydration after fetch join on entity with composite primary key](doctrine#5975)
- [5989: `SimpleObjectHydrator` produces wrong values with inheritance table and simple array type](doctrine#5989)
- [6001: Make second level cache query cache rely on entity region timestamp](doctrine#6001)
- [6004: Fix hydration in a joined inheritance with simple array or json array](doctrine#6004)

Total issues resolved: **1**

- [1568: Identifier is cached with wrong type](doctrine#1568 PGP SIGNATURE-----
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Total issues resolved: **4**

- [1572: Target entity resolver for DQL](doctrine#1572)
- [1573: Merge entity associated to versioned entity](doctrine#1573)
- [4884: DDC-4019: Proxy generator is not including PHP7 return type hints](doctrine#4884)
- [5547: Correcting minor test case incompatibility with XDebug 2.4.x](doctrine#5547)

<h2> Bug

</h2>
<ul>
<li>[<a href='http://www.doctrine-project.org/jira/browse/DDC-3677'>DDC-3677</a>] -         [doctrineGH-1375] DDC-3671 prevent duplicate unique index
</li>
<li>[<a href='http://www.doctrine-project.org/jira/browse/DDC-3899'>DDC-3899</a>] -         [doctrineGH-1507] Fixed wrong property name
</li>
<li>[<a href='http://www.doctrine-project.org/jira/browse/DDC-3908'>DDC-3908</a>] -         [doctrineGH-1510] Fix cache storage related test issues (due to doctrine/cache 1.5.0 changes)
</li>
<li>[<a href='http://www.doctrine-project.org/jira/browse/DDC-3911'>DDC-3911</a>] -         [doctrineGH-1512] Backport of &quot;LimitSubqueryOutputWalker: fix aliasing of property in OrderBy from MappedSuperclass&quot;
</li>
<li>[<a href='http://www.doctrine-project.org/jira/browse/DDC-3973'>DDC-3973</a>] -         [doctrineGH-1540] [DDC-3711] Correct Error on manyToMany with composite primary key + add Tests
</li>
</ul>

<h2>        Documentation
</h2>
<ul>
<li>[<a href='http://www.doctrine-project.org/jira/browse/DDC-3938'>DDC-3938</a>] -         [doctrineGH-1529] Update Upgrade.md after minor bc break in 2.5.1
</li>
</ul>