public static TBuilder SelectUsing <TRequest, TEntity, TBuilder>(
     this CrudRequestEntityConfigBuilderCommon <TRequest, TEntity, TBuilder> config,
     Expression <Func <TRequest, TEntity, bool> > selector)
     where TEntity : class
     where TBuilder : CrudRequestEntityConfigBuilderCommon <TRequest, TEntity, TBuilder>
 {
     return(config.SelectWith(builder => builder.Single(selector)));
 }
 public static TBuilder SelectUsing <TRequest, TEntity, TBuilder, TKey>(
     this CrudRequestEntityConfigBuilderCommon <TRequest, TEntity, TBuilder> config,
     Expression <Func <TRequest, IEnumerable <TKey> > > requestEnumerableExpr,
     Expression <Func <TEntity, TKey> > entityKeyExpr)
     where TEntity : class
     where TBuilder : CrudRequestEntityConfigBuilderCommon <TRequest, TEntity, TBuilder>
 {
     return(config.SelectWith(builder => builder.Collection(requestEnumerableExpr, entityKeyExpr)));
 }