public static object GetExpressionValue(this DbExpression exp)
{
if (exp.NodeType == DbExpressionType.Constant)
{
return(((DbConstantExpression)exp).Value);
}
if (exp.NodeType == DbExpressionType.MemberAccess)
{
DbMemberExpression m = (DbMemberExpression)exp;
object instance = null;
if (m.Expression != null)
{
instance = DbExpressionExtensions.GetExpressionValue(m.Expression);
/* 非静态成员，需要检查是否为空引用。Nullable<T>.HasValue 的情况比较特俗，暂不考虑 */
Type declaringType = m.Member.DeclaringType;
if (declaringType.IsClass || declaringType.IsInterface)
{
if (instance == null)
{
throw new NullReferenceException(string.Format("There is an object reference not set to an instance of an object in expression tree.The type of null object is '{0}'.", declaringType.FullName));
}
}
}
return(GetMemberAccessExpressionValue(m, instance));
}
throw new NotSupportedException();
}
static void Method_Contains(DbMethodCallExpression exp, SqlGenerator generator)
{
MethodInfo method = exp.Method;
if (method.DeclaringType == UtilConstants.TypeOfString)
{
Method_String_Contains(exp, generator);
return;
}
List <DbExpression> exps = new List <DbExpression>();
IEnumerable values = null;
DbExpression arg = null;
var declaringType = method.DeclaringType;
if (typeof(IList).IsAssignableFrom(declaringType) || (declaringType.IsGenericType && typeof(ICollection <>).MakeGenericType(declaringType.GetGenericArguments()).IsAssignableFrom(declaringType)))
{
DbMemberExpression memberExp = exp.Object as DbMemberExpression;
if (memberExp == null || !memberExp.CanEvaluate())
{
throw new NotSupportedException(exp.ToString());
}
values = DbExpressionExtensions.GetExpressionValue(memberExp) as IEnumerable; //Enumerable
arg = exp.Arguments.First();
goto constructInState;
}
if (method.IsStatic && declaringType == typeof(Enumerable) && exp.Arguments.Count == 2)
{
DbMemberExpression memberExp = exp.Arguments.First() as DbMemberExpression;
if (memberExp == null || !memberExp.CanEvaluate())
{
throw new NotSupportedException(exp.ToString());
}
values = DbExpressionExtensions.GetExpressionValue(memberExp) as IEnumerable;
arg = exp.Arguments.Skip(1).First();
goto constructInState;
}
throw UtilExceptions.NotSupportedMethod(exp.Method);
constructInState:
foreach (object value in values)
{
if (value == null)
{
exps.Add(DbExpression.Constant(null, arg.Type));
}
else
{
exps.Add(DbExpression.Parameter(value));
}
}
In(generator, exps, arg);
}
/// <summary>
/// 对 memberExpression 进行求值
/// </summary>
/// <param name="exp"></param>
/// <returns>返回 DbParameterExpression</returns>
public static DbParameterExpression ParseToParameterExpression(this DbMemberExpression memberExpression)
{
DbParameterExpression ret = null;
//求值
object val = DbExpressionExtensions.GetExpressionValue(memberExpression);
ret = DbExpression.Parameter(val, memberExpression.Type);
return(ret);
}
