/// <summary>
/// Returns a query that will return an Empty enumeration of specified type when executed.
/// </summary>
/// <param name="entityType"></param>
/// <returns></returns>
public static EntityQuery BuildEmptyQuery(Type entityType)
{
var parameterExpr = Expression.Parameter(entityType, "t");
// where 1 = 0;
var predicateExpr = Expression.Equal(Expression.Constant(1), Expression.Constant(0));
var lambdaExpr = Expression.Lambda(predicateExpr, parameterExpr);
var entityQuery = EntityQuery.Create(entityType);
entityQuery = AddWhereClause(entityQuery, lambdaExpr);
return(entityQuery);
}
/// <summary>
/// Builds an <see cref="EntityQuery"/> based on a collection of <see cref="EntityKey"/>s.
/// The EntityQuery returned is actually an EntityQuery{T} but T is unknown at compile time.
/// </summary>
/// <param name="keys"></param>
/// <returns></returns>
public static EntityQuery BuildQuery(IEnumerable <EntityKey> keys)
{
if (!keys.AllEqual(k => k.EntityType))
{
throw new ArgumentException("The EntityQueryBuilder.BuildQuery method requires that the 'keys' parameter consist of EntityKeys all with the same EntityType.");
}
var firstKey = keys.FirstOrDefault();
if (firstKey == null)
{
return(null);
}
var entityQuery = EntityQuery.Create(firstKey.EntityType.ClrType);
return(AddWhereClause(entityQuery, keys));
}
