Relations are one of the features which allows rather advance querying capabilities in eZ Publish/Platform, however at the moment they are missing and only options are using FieldRelation criterion, and methods on ContentService that are not optimal for large amounts of data.

The RelationCriterion could match related content for the parameters src version (srcContentId, srcVersionId) and optional RelationType and fieldId. The ReverseRelationCriterion matches the reverse related content for a given contentId with optional parameter RelationType.

NB:

• Native "Assets" functionality would imply support for this in relationType, and possibility to limit to a specific asset type

Related:

• Consider if this should take on scope from FieldRelation or not, hence deprecate it
• Consider to add offset and limit to ContentService loadRelations (and use in REST implemntation) and loadReverseRelations