Gets whether this member is part of the type's identity.
Assembly: System.Data.Linq (in System.Data.Linq.dll)
If this property is true, the class member represents a column that is part of the table’s unique key. More than one member of the class can have this property set to true for a key that is a composite of the associated columns. For an entity class, at least one member must have this attribute and should be mapped to the primary key or a unique key in the corresponding table or view. Otherwise, LINQ to SQL considers instances of the class as read-only for the purpose of submitting changes to the database.
The set of columns identified with are not required to be the primary key. They simply denote a set that uniquely identifies the entity. Common alternatives include clustering index columns or other unique key columns.