我正在尝试完成 Todd Sprang 提供的动态查询的实现,请参阅此 link 。 目前我正在尝试按 DateTime 类型启用过滤,并且我正在努力使用“大于”和“小于”运算符来创建 lambda 表达式,因此我的 SQL 将显示为“WHERE someDate<='2017-04-27 00: 00:00' AND someDate<='2017-04-27 23:59:59'。
我设法提取了一个运算符方法:
private static readonly MethodInfo DateTimeGreaterThanOrEqualMethod = typeof(DateTime).GetMethod("op_GreaterThanOrEqual",
BindingFlags.Static | BindingFlags.Public);
private static readonly MethodInfo DateTimeLessThanOrEqualMethod = typeof(DateTime).GetMethod("op_LessThanOrEqual",
BindingFlags.Static | BindingFlags.Public);
这是我的 DateTime lambda 过滤器方法:
private static Expression<Func<TDbType, bool>> ApplyDateTimeCriterion<TDbType,
TSearchCriteria>(TSearchCriteria searchCriteria, PropertyInfo searchCriterionPropertyInfo,
Type dbType, MemberInfo dbFieldMemberInfo, Expression<Func<TDbType, bool>> predicate)
{
var searchDateTime = searchCriterionPropertyInfo.GetValue(searchCriteria) as DateTime?;
if (searchDateTime == null)
{
return predicate;
}
var valueDateMin = ((DateTime)searchDateTime).Date;
var valueDateMax = new DateTime(valueDateMin.Year, valueDateMin.Month, valueDateMin.Day, 23, 59, 59);
var dbTypeParameter = Expression.Parameter(dbType, @"x");
var dbFieldMember = Expression.MakeMemberAccess(dbTypeParameter, dbFieldMemberInfo);
var criterionConstantMin = new Expression[] { Expression.Constant(valueDateMin) };
var criterionConstantMax = new Expression[] { Expression.Constant(valueDateMax) };
//having problem down here, when trying to call static method which needs two parameters
var greaterThanCall = Expression.Call(dbFieldMember, DateTimeGreaterThanOrEqualMethod, criterionConstantMin);
var lambdaGreaterThan = Expression.Lambda(greaterThanCall, dbTypeParameter) as Expression<Func<TDbType, bool>>;
var lessThanCall = Expression.Call(dbFieldMember, DateTimeLessThanOrEqualMethod, criterionConstantMax);
var lambdaLessThan = Expression.Lambda(greaterThanCall, dbTypeParameter) as Expression<Func<TDbType, bool>>;
return predicate.And(lambdaGreaterThan).And(lambdaLessThan);
}
我在调用 Expression.Call 时遇到问题,因为 op_GreaterThanOrEqual 是带有 2 个参数的静态方法。也许我不应该调用 op_GreaterThanOrEqual,也许这必须以另一种方式完成?
最佳答案
I am having problem on calling Expression.Call because op_GreaterThanOrEqual is a static method with 2 parameters
Expression.Call
有多个重载,您需要为静态方法使用正确的重载(当前您正在使用带有 instance
参数的重载,因此为实例方法) .
也不要创建不必要的Expression[]
(接收多个表达式的方法通常使用params Expression[]
,因此会在需要时为您创建) :
var criterionConstantMin = Expression.Constant(valueDateMin);
var criterionConstantMax = Expression.Constant(valueDateMax);
这是有问题的电话
var greaterThanCall = Expression.Call(DateTimeGreaterThanOrEqualMethod, dbFieldMember, criterionConstantMin);
var lessThanCall = Expression.Call(DateTimeLessThanOrEqualMethod, dbFieldMember, criterionConstantMax);
maybe this has to be done in another way?
有特定的Expression
方法,例如GreaterThan等对应于每个 C# 比较运算符,因此您不必费心获取运算符方法信息等,只需使用:
var greaterThanCall = Expression.GreaterThanOrEqual(dbFieldMember, criterionConstantMin);
var lessThanCall = Expression.LessThanOrEqual(dbFieldMember, criterionConstantMax);
更新:为了支持 DateTime?
成员,请使用以下内容:
var criterionConstantMin = Expression.Constant(valueDateMin, dbFieldMember.Type);
var criterionConstantMax = Expression.Constant(valueDateMax, dbFieldMember.Type);
然后
var greaterThanCall = Expression.GreaterThanOrEqual(dbFieldMember, criterionConstantMin);
var lessThanCall = Expression.LessThanOrEqual(dbFieldMember, criterionConstantMax);
关于c# - 使用日期时间筛选器构建 LINQ to Entities 表达式树,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/43649673/