Write something about all FAQ entries that were empty
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Benjamin Eberlei
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@ -13,7 +13,8 @@ Entity Classes
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I access a variable and its null, what is wrong?
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Proxy, not use public. Private and protected variables instead.
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If this variable is a public variable then you are violating one of the criteria for entities.
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All properties have to be protected or private for the proxy object pattern to work.
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How can I add default values to a column?
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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@ -41,7 +42,18 @@ Mapping
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Why do I get exceptions about unique constraint failures during ``$em->flush()``?
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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-
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Doctrine does not check if you are re-adding entities with a primary key that already exists
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or adding entities to a collection twice. You have to check for both conditions yourself
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in the code before calling ``$em->flush()`` if you know that unique constraint failures
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can occur.
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In `Symfony 2<http://www.symfony.com>`_ for example there is a Unique Entity Validator
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to achieve this task.
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For collections you can check with ``$collection->contains($entity)`` if an entity is already
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part of this collection. For a FETCH=LAZY collection this will initialize the collection,
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however for FETCH=EXTRA_LAZY this method will use SQL to determine if this entity is already
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part of the collection.
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Associations
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------------
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@ -49,32 +61,64 @@ Associations
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What is wrong when I get an InvalidArgumentException "A new entity was found through the relationship.."?
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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This exception is thrown during ``EntityManager#flush()`` when there exists an object in the identity map
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that contains a reference to an object that Doctrine does not know about. Say for example you grab
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a "User"-entity from the database with a specific id and set a completly new object into one of the associations
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of the User object. If you then call ``EntityManager#flush()`` without letting Doctrine know about
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this new object using ``EntityManager#persist($newObject)`` you will see this exception.
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You can solve this exception by:
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* Calling ``EntityManager#persist($newObject)`` on the new object
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* Using cascade=persist on the association that contains the new object
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How can I filter an association?
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Natively you can't in 2.0 and 2.1. You should use DQL queries to query for the filtered set of entities.
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Natively you can't filter associations in 2.0 and 2.1. You should use DQL queries to query for the filtered set of entities.
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I call clear() on a One-To-Many collection but the entities are not deleted
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.
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This is an expected behavior that has to do with the inverse/owning side handling of Doctrine.
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By definition a One-To-Many association is on the inverse side, that means changes to it
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will not be recognized by Doctrine.
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If you want to perform the equivalent of the clear operation you have to iterate the
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collection and set the owning side many-to-one reference to NULL aswell to detach all entities
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from the collection. This will trigger the appropriate UPDATE statements on the database.
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How can I add columns to a many-to-many table?
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.
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The many-to-many association is only supporting foreign keys in the table definition
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To work with many-to-many tables containing extra columns you have to use the
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foreign keys as primary keys feature of Doctrine introduced in version 2.1.
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See :doc:`the tutorial on composite primary keys for more information<../tutorials/composite-primary-keys>`.
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How can i paginate fetch-joined collections?
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.
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If you are issuing a DQL statement that fetches a collection as well you cannot easily iterate
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over this collection using a LIMIT statement (or vendor equivalent).
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Doctrine does not offer a solution for this out of the box but there are several extensions
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that do:
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* `DoctrineExtensions <http://github.com/beberlei/DoctrineExtensions>`_
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* `Pagerfanta <http://github.com/whiteoctober/pagerfanta>`_
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Why does pagination not work correctly with fetch joins?
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.
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Pagination in Doctrine uses a LIMIT clause (or vendor equivalent) to restrict the results.
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However when fetch-joining this is not returning the correct number of results since joining
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with a one-to-many or many-to-many association muliplies the number of rows by the number
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of associated entities.
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See the previous question for a solution to this task.
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Inheritance
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-----------
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@ -82,7 +126,10 @@ Inheritance
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Can I use Inheritance with Doctrine 2?
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.
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Yes, you can use Single- or Joined-Table Inheritance in Doctrine 2.
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See the documentation chapter on :doc:`inheritance mapping <inheritance-mapping>`_ for
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the details.
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EntityGenerator
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---------------
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@ -95,10 +142,6 @@ Why does the EntityGenerator not do X?
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Why does the EntityGenerator not generate inheritance correctly?
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.
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.
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Performance
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@ -107,13 +150,30 @@ Performance
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Why is an extra SQL query executed every time I fetch an entity with a one-to-one relation?
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.
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If Doctrine detects that you are fetching an inverse side one-to-one association
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it has to execute an additional query to load this object, because it cannot know
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if there is no such object (setting null) or if it should set a proxy and which id this proxy has.
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To solve this problem currently a query has to be executed to find out this information.
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Doctrine Query Language
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-----------------------
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What is DQL and why does it have such a strange syntax?
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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What is DQL?
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~~~~~~~~~~~~
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DQL stands for Doctrine Query Language, a query language that very much looks like SQL
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but has some important benefits when using Doctrine:
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* It uses class names and fields instead of tables and columns, separating concerns between backend and your object model.
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* It utilizes the metadata defined to offer a range of shortcuts when writing. For example you do not have to specify the ON clause of joins, since Doctrine already knows about them.
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* It adds some functionality that is related to object management and transforms them into SQL.
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It also has some drawbacks of course:
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* The syntax is slightly different to SQL so you have to learn and remember the differences.
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* To be vendor independent it can only implement a subset of all the existing SQL dialects. Vendor specific functionality and optimizations cannot be used through DQL unless implemented by you explicitly.
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* For some DQL constructs subselects are used which are known to be slow in MySQL.
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Can I sort by a function (for example ORDER BY RAND()) in DQL?
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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