/// <summary>
 /// Directly adds a constraint by a collection of <see cref="IEntityCollection"/> keys.
 /// </summary>
 /// <param name="builder">
 /// The builder.
 /// </param>
 /// <param name="collectionKeys">
 /// The collection keys.
 /// </param>
 /// <returns>
 /// The <see cref="IProductContentQueryBuilder"/>.
 /// </returns>
 public static IProductContentQueryBuilder ConstrainByCollectionKey(this IProductContentQueryBuilder builder, IEnumerable<Guid> collectionKeys)
 {
     builder.AddCollectionKeyConstraint(collectionKeys);
     return builder;
 }
 /// <summary>
 /// Directly adds a constraint by a <see cref="IEntityCollection"/> key.
 /// </summary>
 /// <param name="builder">
 /// The builder.
 /// </param>
 /// <param name="collectionKey">
 /// The collection key.
 /// </param>
 /// <returns>
 /// The <see cref="IProductContentQueryBuilder"/>.
 /// </returns>
 /// <remarks>
 /// Filters and Collections are actually both <see cref="IEntityCollection"/>s and the underlying query just uses the 
 /// collection key(s) so they can be added directly.
 /// </remarks>
 public static IProductContentQueryBuilder ConstrainByCollectionKey(this IProductContentQueryBuilder builder, Guid collectionKey)
 {
     builder.AddCollectionKeyConstraint(collectionKey);
     return builder;
 }