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Dynamics CRM 2011 How To

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How to get all the entities in a one to many relationship (C#)

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I had an entity which had a one to many relationship with a second entity, those second entities were listed on a sub-grid on a form and I needed a way to get those entities in a plugin.

The idea is straight forward, query the relationship between the entity and the entities in the sub-grid.

So, given the Entity, the logical name of the related entity and the logical name of the relationship the following function will return a EntityCollection of the related entities:

public EntityCollection ListRelatedEntities(Entity parent,
string relationshipLogicalName, string relatedEntity)
{
    // The relationship both (i.) defines the
    // relationship to the 'relatedEntity' and
    // (ii.) acts as a key into responses back.
    Relationship relationship = new Relationship()
    {
        SchemaName = relationshipLogicalName
    };
    RelationshipQueryCollection relatedEntityCollection = new RelationshipQueryCollection();
    relatedEntityCollection.Add(relationship,
        new QueryExpression()
        {
            EntityName = relatedEntity,
            ColumnSet = new ColumnSet(true)
        });

    RetrieveRequest request = new RetrieveRequest()
    {
        RelatedEntitiesQuery = relatedEntityCollection,
        ColumnSet = new ColumnSet(true),
        Target = new EntityReference
        {
            Id = parent.Id,
            LogicalName = parent.LogicalName
        }
    };

    RetrieveResponse response = (RetrieveResponse)this._crmService.Execute(request);
    if (response == null) return null;
    if (response.Entity == null) return null;
    return response.Entity.RelatedEntities[relationship];
}

The above should work for both an N:N relationship as well as a 1:N relationship.

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These notes have been tested with Microsoft Dynamics CRM 2011, and may apply to other versions as well.