Creating Records for Many to Many Relationship in MS CRM

Have you ever created Many to Many Relationship in MS CRM 4.0 ?

Use AssociateEntitiesRequest Class (CrmService)
Contains the data needed to add a link between two entity instances in a many-to-many relationship.
When you create Many to Many Relationship between two entities (system / Custom), MS CRM 4.0 creates New Table in MS CRM database. The name would be the "Relationship name" which you specified while creating Many to Many relationship.

Now, how do u associate a record to Entities?

Let's say, You have One "Entity: Contact" and other "Entity: New_CustomEntity".

Step 1: Create the record for first "Entity: Contact" (you will get a GUID for this record)

Step 2: Create the record for Second "Entity: New_CustomEntity" (you will get a GUID for this record)

Step 3: When you create Many to Many Relationship between two entities, you will specify "Relationship name" Eg: Contact_New_CustomEntity_ManyToMany

Step 4: Call below method and pass both the Entity Information with Relationship name. For more info see below example.

// Code Create Moniker for first Entity: Contact
Moniker Moniker1 = new Moniker();
Moniker1.Id = new Guid("SPECIFY GUID For the record");
Moniker1.Name = EntityName.contact.ToString(); 

// Code Create Moniker for second Entity: New_CustomEntity
Moniker Moniker2 = new Moniker();
Moniker2.Id = new Guid("SPECIFY GUID For the record");
Moniker2.Name = EntityName.New_CustomEntity.ToString(); 

string strManyToManyRelationshipName = "Contact_New_CustomEntity_ManyToMany"; 

if (ObjCrmHelper.AssociateManyToManyEntityRecords(Moniker1, Moniker2, strManyToManyRelationshipName))
    MessageBox.Show("Associated Entities Record.");
else
    MessageBox.Show("Error Occoured."); 

//Method which will associate the records.
public bool AssociateManyToManyEntityRecords(Moniker Moniker1, Moniker Moniker2, string strEntityRelationshipName)
{
    try
    {
        // Create an AssociateEntities request.
        AssociateEntitiesRequest request = new AssociateEntitiesRequest();

        // Set the ID of Moniker1 to the ID of the lead.
        request.Moniker1 = Moniker1;  

        // Set the ID of Moniker2 to the ID of the contact.
        request.Moniker2 = Moniker2; 

        // Set the relationship name to associate on.
        request.RelationshipName = strEntityRelationshipName;

        // Execute the request.
        Service.Execute(request); 

        return true;
    }  

    catch (SoapException ex)
    {
        return false;
    }

}

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Happy Coding !!!!!!