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LINQ2SQL表达式-转换日期时转换失败

linq-to-sql lambda c#

Muflix · 技术社区 · 7 年前

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

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

我把这个表达式叫做

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):从字符串转换日期和/或时间时转换失败。

这很有效

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

LaunchWeekStartDate的数据库列和类属性的类型为DateTime。

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

请你解释一下这里的问题是什么?

而不是 Express.Equal Express.Call 具有 CompareTo

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);

System.ArgumentException:类型为“System.Int32”的表达式不能用于返回类型“System.Boolean”

1 回复 | 直到 7 年前

Wizzyno 5 年前

在这篇帖子上查看我的答案 here

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

Muflix 7 年前

这很有效,我是从这个9年的博客上抄来的 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,这项任务有点复杂。

我也不知道,怎么做 GreaterThan 和 LessThen 采用这种方法:/

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);