EntityCollection<TEntity>.Add(TEntity) Method

Definition

Namespace:

System.Data.Objects.DataClasses

Assembly:

System.Data.Entity.dll

Adds an object to the collection.

public:
 virtual void Add(TEntity entity);

public void Add (TEntity entity);

override this.Add : 'Entity -> unit

Public Sub Add (entity As TEntity)

Parameters

entity

TEntity

An object to add to the collection. entity must implement IEntityWithRelationships.

Implements

Add(T)

Exceptions

ArgumentNullException

entity is null.

Examples

This example is based on the Adventure Works Sales Model. To run the code in this example, you must have already added the AdventureWorks Sales Model to your project and configured your project to use the Entity Framework. To do this, complete the procedures in How to: Manually Configure an Entity Framework Project and How to: Manually Define the Model and Mapping Files.

This example creates two new SalesOrderHeader entities, adds them to the Contact entity, and, after removing an object, uses the Add method to add the object back to the collection.

using (AdventureWorksEntities context =
    new AdventureWorksEntities())
{
    Contact contact = new Contact();

    // Create a new SalesOrderHeader.
    SalesOrderHeader newSalesOrder1 = new SalesOrderHeader();
    // Add SalesOrderHeader to the Contact.
    contact.SalesOrderHeaders.Add(newSalesOrder1);

    // Create another SalesOrderHeader.
    SalesOrderHeader newSalesOrder2 = new SalesOrderHeader();
    // Add SalesOrderHeader to the Contact.
    contact.SalesOrderHeaders.Add(newSalesOrder2);

    // Get all related ends
    IEnumerable<IRelatedEnd> relEnds =
        ((IEntityWithRelationships)contact)
        .RelationshipManager.GetAllRelatedEnds();

    foreach (IRelatedEnd relEnd in relEnds)
    {
        // Get Entity Collection from related end
        EntityCollection<SalesOrderHeader> entityCollection =
            (EntityCollection<SalesOrderHeader>)relEnd;

        Console.WriteLine("EntityCollection count: {0}",
            entityCollection.Count);
        // Remove the first entity object.
        entityCollection.Remove(newSalesOrder1);

        bool contains = entityCollection.Contains(newSalesOrder1);

        // Write the number of items after one entity has been removed
        Console.WriteLine("EntityCollection count after one entity has been removed: {0}",
            entityCollection.Count);

        if (contains == false)
            Console.WriteLine("The removed entity is not in in the collection any more.");

        //Use IRelatedEnd to add the entity back.
        relEnd.Add(newSalesOrder1);
        Console.WriteLine("EntityCollection count after an entity has been added again: {0}",
            entityCollection.Count);
    }
}

Remarks

The Add method adds an object to an EntityCollection<TEntity> and creates a relationship between the two objects. When the source object is attached to an ObjectContext instance, the Add method also adds the object to the ObjectContext. This operation is translated into an insert operation in the data source when SaveChanges is called. For more information, see Creating, Adding, Modifying, and Deleting Objects.

The Add method can be called multiple times on the same object instance.