LINQ2SQL 表达式 - 转换日期时转换失败

Question

我有这个 Linq 表达式

var searchDate = DateTime.ParseExact("17.12.2018", "dd.MM.yyyy", 
                                      CultureInfo.InvariantCulture, 
                                      DateTimeStyles.None);

result = result.Where(DatePredicate("LaunchWeekStartDate", searchDate, 3));

我称这个表达式为

public static Expression<Func<General, bool>> DatePredicate(string columnName, 
                                                            DateTime 
                                                            searchValue, 
                                                            int? operatorId)
{
  var type = typeof(General);
  var x = Expression.Parameter(type, "x");
  var member = Expression.Property(x, columnName);
  Expression expression;

  var constant = Expression.Constant(searchValue, typeof(DateTime));

  // Greater Than >
  if (operatorId == 2)
  {
    expression = Expression.GreaterThan(member, constant); // THIS THROW ERROR
    return Expression.Lambda<Func<General, bool>>(expression, x);
  }

  // Less Than <
  else if (operatorId == 4)
  {
    expression = Expression.LessThan(member, constant); // THIS THROW ERROR
    return Expression.Lambda<Func<General, bool>>(expression, x);
  }

  // Equal
  var column = type.GetProperties().FirstOrDefault(p => p.Name == columnName);

  expression = column == null
             ? expression = Expression.Constant(true) // THIS WORKS
             : expression = Expression.Equal(member, constant); // THIS THROW ERROR

  return Expression.Lambda<Func<General, bool>>(expression, x);
}

我得到的错误是

System.Data.SqlClient.SqlException (0x80131904): Conversion failed when converting date and/or time from character string.

这有效

var searchDate = DateTime.ParseExact("17.12.2018", "dd.MM.yyyy", 
                                     CultureInfo.InvariantCulture, 
                                     DateTimeStyles.None);
result = result.Where(x => x.LaunchWeekStartDate == searchDate);

LaunchWeekStartDate 的数据库列和 class 属性是 DateTime 类型。

public class General
    {
        [Key]
        public Int64 RowNumber {get; set;}
    // ...
        public DateTime LaunchWeekStartDate { get; set; }
    }

拜托，你能解释一下这里的问题是什么吗？

编辑：

我尝试使用 Express.Call 和 CompareTo 方法，而不是 Express.Equal。

var member = Expression.Property(x, columnName);
MethodInfo method = typeof(DateTime).GetMethod("CompareTo", new[] { typeof(DateTime) });
constant = Expression.Constant(searchValue, typeof(DateTime));
var call = Expression.Call(member, method, constant);
return Expression.Lambda<Func<General, bool>>(call, x);

但是我遇到了一个我不明白的异常：

System.ArgumentException: Expression of type 'System.Int32' cannot be used for return type 'System.Boolean'

Answer 1

这有效，我从这个 9 年前的博客中复制了它 https://www.tabsoverspaces.com/231060-comparing-date-only-in-ef

expression = Expression.And(
                Expression.Equal(
                    Expression.MakeMemberAccess(member, typeof(DateTime).GetMember("Day").Single()),
                    Expression.Constant(searchValue.Day)
                    ),
                Expression.And(
                    Expression.Equal(
                        Expression.MakeMemberAccess(member, typeof(DateTime).GetMember("Month").Single()),
                        Expression.Constant(searchValue.Month)
                        ),
                    Expression.Equal(
                        Expression.MakeMemberAccess(member, typeof(DateTime).GetMember("Year").Single()),
                        Expression.Constant(searchValue.Year)
                        )
                    )
                );

但在我看来，这样的任务有点复杂。

我也不知道如何用这种方法制作 GreaterThan 和 LessThen :/

编辑： 现在它也适用于大于和小于

// Greater Than >
expression = Expression.GreaterThan(Expression.MakeMemberAccess(member, typeof(DateTime).GetMember("Date").Single()), constant);

// Less Than <
expression = Expression.LessThan(Expression.MakeMemberAccess(member, typeof(DateTime).GetMember("Date").Single()), constant);

// Equal
expression = Expression.Equal(Expression.MakeMemberAccess(member, typeof(DateTime).GetMember("Date").Single()), constant);

Answer 2

查看我对此的回答 post here

解决方案是如何使 EntityFramework 生成带参数的 SqlCommand，以便数据类型映射可以将 CLR DateTime 转换为 SQL 服务器等效项。

LINQ2SQL 表达式 - 转换日期时转换失败

LINQ2SQL Expression - Conversion failed when converting date

c#

lambda

linq-to-sql