Many-to-many, polymorphic, one-to-one, and nested relations with configurable cascade actions.

Advanced Relations

FastCMS supports advanced relationship types with configurable cascade actions.

Status: Schema validation works for all relation types. Runtime enforcement of many-to-many, polymorphic, and cascade actions is pending.

Relation Types

Type	Description
`many-to-one`	Multiple records reference one parent (default)
`one-to-many`	One record can have many related records
`many-to-many`	Records relate to multiple records in both directions
`one-to-one`	Each record relates to exactly one other
`polymorphic`	Relate to records from multiple collections

Cascade Actions

Action	Behavior
`restrict`	Prevent deletion if related records exist (default)
`cascade`	Delete related records automatically
`set_null`	Set foreign key to NULL when parent is deleted
`no_action`	Standard SQL — may leave orphaned records

Relation Schema Options

{
  "name": "author",
  "type": "relation",
  "relation": {
    "collection_id": "users",
    "type": "many-to-one",
    "cascade_delete": "restrict",
    "display_fields": ["name", "email"],
    "max_depth": 2
  }
}

Field	Description	Default
`collection_id`	Target collection ID	Required
`collection_ids`	Target collection IDs (for polymorphic)	null
`type`	Relationship type	`one-to-many`
`cascade_delete`	Action on parent deletion	`restrict`
`display_fields`	Fields to show in relation	`["id"]`
`max_depth`	Nested loading depth (0–5)	1
`junction_table`	Junction table for many-to-many	null
`junction_field`	Field referencing this collection	null
`target_field`	Field referencing target collection	null

Examples

Many-to-One (Posts → Author)

{
  "name": "author",
  "type": "relation",
  "relation": {
    "collection_id": "users",
    "type": "many-to-one",
    "cascade_delete": "set_null",
    "display_fields": ["name", "email"]
  }
}

One-to-Many (Post → Comments)

{
  "name": "post",
  "type": "relation",
  "relation": {
    "collection_id": "posts",
    "type": "one-to-many",
    "cascade_delete": "cascade",
    "display_fields": ["title"]
  }
}

Many-to-Many (Posts ↔ Tags)

{
  "name": "tags",
  "type": "relation",
  "relation": {
    "collection_id": "tags",
    "type": "many-to-many",
    "junction_table": "posts_tags",
    "junction_field": "post_id",
    "target_field": "tag_id",
    "display_fields": ["name"]
  }
}

Polymorphic (Comments on Posts or Events)

{
  "name": "commentable",
  "type": "relation",
  "relation": {
    "collection_ids": ["posts", "events"],
    "type": "polymorphic",
    "polymorphic_type_field": "commentable_type",
    "display_fields": ["title"]
  }
}

Choosing Cascade Actions

// Comments should be deleted with their post
{"cascade_delete": "cascade"}

// Posts should persist when author is deleted
{"cascade_delete": "set_null"}

// Can't delete if dependencies exist
{"cascade_delete": "restrict"}

Current Limitations

Feature	Status
Schema validation	✅
Basic one-to-many expansion	✅
Automatic junction tables	⏳ Pending
Polymorphic querying	⏳ Pending
Recursive loading (depth > 1)	⏳ Pending
Cascade action enforcement	⏳ Pending

Advanced Relations

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