FieldDefinitionInterface should include a getTargetEntityTypeId()

Easy task

Yup. Thanks!

+1 on "target" too, for the reason @fago mentioned, + I advocate to keep TypedData API as "in the back" as possible, so I'm not too keen on modelling domain interfaces on it :-)

Temptatively setting back to RTBC ?

@webchick:

$body_field->entityType() == 'field_entity' (method from EntityInterface - you're an entity, what's your entity type ?)
$body_field->getTargetEntityType() == 'node' (method from FieldInterface - you're a field, which entity type are you attached to ?)

More broadly speaking:
- There are a lot of config entities that store something "related to an entity type", possibly related to "a specific bundle in this entity type".
- Those typically have 'entity_type' / 'bundle' properties in their CMI file, resulting in $entity_type / $bundle members in the corresponding ConfigEntity classes.
- We're looking for good accessor method names for those properties, considering that, by virtue of being a ConfigEntity, there already are entityType() / bundle() methods (for "what is *your own* entity type / bundle as an Entity).

Ideally each ConfigEntity that fits that pattern should not have to come up with its own method names. getHostEntityType() might kinda sorta work for fields since you could say that a field "is hosted" by an entity type (even though we currently don't use that specific terminology anywhere in code / comments / UI, so that would still feel weird IMO). But "hosted by" seems totally unfit to qualify the relation between, for example, an EntityDisplay and the entity type/bundle it is associated with.

In that sense, getTargetEntityType() / getTargetBundle() feel more neutral. "Those are the entity type & bundle I, as a piece of configuration, am talking about".

#19 works for me.

Suggestion to address @webchick's request in #18:

FieldDefinitionInterface::getTargetEntityType():

Returns the entity type this field is attached to.

This method should not be confused with EntityInterface::entityType() (configurable fields are config entities, and thus implement both interfaces):
- FieldDefinitionInterface::getTargetEntityType() answers "as a field, which entity type are you attached to ?", 
- EntityInterface::entityType() answers "as a (config) entity, what is your own entity type"

@return ...

?

getAttachedToEntityType() ? hardly seems a win, it's ugly and doesn't mean anything...

1. +++ b/core/lib/Drupal/Core/Entity/EntityManager.php
   @@ -332,8 +332,12 @@ public function getFieldDefinitions($entity_type, $bundle = NULL) {
   +        $base_definitions = $class::baseFieldDefinitions($entity_type);
   +        foreach ($base_definitions as &$base_definition) {
   +          $base_definition['entity_type'] = $entity_type;
   +        }
            $this->entityFieldInfo[$entity_type] = array(
   -          'definitions' => $class::baseFieldDefinitions($entity_type),
   +          'definitions' => $base_definitions,
   

   This looks wrong ? $base_definition is a FieldDefinition object, not an array ?

2. +++ b/core/modules/field/lib/Drupal/field/Entity/FieldInstance.php
   @@ -586,6 +586,7 @@ public function isConfigurable() {
      /**
       * {@inheritdoc}
       */
   +
      public function isDisplayConfigurable($context) {
        return TRUE;
   

   Oops.

There are currently no setters on FieldDefinitionInterface, because FeidlDefinitioninterface is too generic (used for base fields, configurable fields, configurable field instances, and there are no setters that make sense for all of those). Separate mess.

baseFieldDefinitions() really returns an array of FieldDefinition objects, not FieldDefinitionInterface...

This being said - FieldDefinition::getTargetEntityType() returns $this->definition['entity_type'], so it doesn't look like $base_definition->entity_type = $entity_type will work.

The previous patch ($base_definition['entity_type'] = $entity_type) did work because FieldDefinition / DataDefinition has an ArrayAccess layer that writes to the protected $this->definition :-/

I'd say we need a setTargetEntityType() method on FieldDefinition...

Looks good to me. Thanks !

Sigh; I suppose this should be getEntityTypeId() now...