Object Reference for Salesforce and Force.com

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Relationships Among Objects

Relationships associate objects with other objects. For example, a relationship can link a custom object to standard object in a related list, such as linking a custom object called Bugs to cases to track product defects associated with customer cases. To view the parent and child relationships among standard objects, see the ERD diagrams in Data Model.

You can use parent-child relationships in SOQL queries. For more information, see Relationship Queries in the Salesforce SOQL and SOSL Reference Guide.

Note

You can define different types of relationships by creating custom relationship fields on an object. The differences between relationship types include how they handle data deletion, record ownership, security, and required fields in page layouts:
  • Master-Detail (1:n) — A parent-child relationship in which the master object controls certain behaviors of the detail object:
    • When a record of the master object is deleted, its related detail records are also deleted.
    • The Owner field on the detail object is not available and is automatically set to the owner of its associated master record. Custom objects on the detail side of a master-detail relationship cannot have sharing rules, manual sharing, or queues, as these require the Owner field.
    • The detail record inherits the sharing and security settings of its master record.
    • The master-detail relationship field is required on the page layout of the detail record.
    • By default, records can’t be reparented in master-detail relationships. Administrators can, however, allow child records in master-detail relationships on custom objects to be reparented to different parent records by selecting the Allow reparenting option in the master-detail relationship definition.
    You can define master-detail relationships between custom objects or between a custom object and a standard object. However, the standard object cannot be on the detail side of a relationship with a custom object. In addition, you cannot create a master-detail relationship in which the User or Lead objects are the master.

    When you define a master-detail relationship, the custom object on which you are working is the detail side. Its data can appear as a custom related list on page layouts for the other object.

  • Many-to-many — You can use master-detail relationships to model many-to-many relationships between any two objects. A many-to-many relationship allows each record of one object to be linked to multiple records from another object and vice versa. For example, you may have a custom object called “Bug” that relates to the standard case object such that a bug could be related to multiple cases and a case could also be related to multiple bugs. To create a many-to-many relationship, simply create a custom junction object with two master-detail relationship fields, each linking to the objects you want to relate. See the Salesforce online help for details.

    Custom objects with two master-detail relationships are supported in API version 11 and later.

  • Lookup (1:n) — This type of relationship links two objects together, but has no effect on deletion or security. Unlike master-detail fields, lookup fields are not automatically required. When you define a lookup relationship, data from one object can appear as a custom related list on page layouts for the other object. See the Salesforce online help for details.

To create relationships, use the user interface or Salesforce Metadata API.