/// <summary>
/// Binds 'cast' function to create a LINQ <see cref="Expression"/>.
/// </summary>
/// <param name="node">The query node to bind.</param>
/// <param name="context">The query binder context.</param>
/// <returns>The LINQ <see cref="Expression"/> created.</returns>
protected virtual Expression BindCastSingleValue(SingleValueFunctionCallNode node, QueryBinderContext context)
{
CheckArgumentNull(node, context, "cast");
Expression[] arguments = BindArguments(node.Parameters, context);
Contract.Assert(arguments.Length == 1 || arguments.Length == 2);
Expression source = arguments.Length == 1 ? context.CurrentParameter : arguments[0];
string targetTypeName = (string)((ConstantNode)node.Parameters.Last()).Value;
IEdmType targetEdmType = context.Model.FindType(targetTypeName);
Type targetClrType = null;
if (targetEdmType != null)
{
IEdmTypeReference targetEdmTypeReference = targetEdmType.ToEdmTypeReference(false);
targetClrType = context.Model.GetClrType(targetEdmTypeReference);
if (source != NullConstant)
{
if (source.Type == targetClrType)
{
return(source);
}
if ((!targetEdmTypeReference.IsPrimitive() && !targetEdmTypeReference.IsEnum()) ||
(context.Model.GetEdmPrimitiveTypeReference(source.Type) == null && !TypeHelper.IsEnum(source.Type)))
{
// Cast fails and return null.
return(NullConstant);
}
}
}
if (targetClrType == null || source == NullConstant)
{
return(NullConstant);
}
if (targetClrType == typeof(string))
{
return(ExpressionBinderHelper.BindCastToStringType(source));
}
else if (TypeHelper.IsEnum(targetClrType))
{
return(BindCastToEnumType(source.Type, targetClrType, node.Parameters.First(), arguments.Length, context));
}
else
{
if (TypeHelper.IsNullable(source.Type) && !TypeHelper.IsNullable(targetClrType))
{
// Make the target Clr type nullable to avoid failure while casting
// nullable source, whose value may be null, to a non-nullable type.
// For example: cast(NullableInt32Property,Edm.Int64)
// The target Clr type should be Nullable<Int64> rather than Int64.
targetClrType = typeof(Nullable <>).MakeGenericType(targetClrType);
}
try
{
return(Expression.Convert(source, targetClrType));
}
catch (InvalidOperationException)
{
// Cast fails and return null.
return(NullConstant);
}
}
}
