包含的LINQ表达式

Question

我想在linq中添加动态表达式,但面对包含方法的问题,它对Equal方法非常有效

问题是我正在FilterField动态地如何在查询中替换

到目前为止,我曾尝试过

List<int> Ids = new List<int>();  
**string filterField ="DEPARTMENT"; ==> Dynamic Field**

var eParam = Expression.Parameter(typeof(EmployeeDetail), "e");

var comparison = Expression.Equal(Expression.Property(eParam, filterField), Expression.Convert(Expression.Constant(Ids), Expression.Property(eParam, filterField).Type));

var lambda = Expression.Lambda<Func<EmployeeDetail, bool>>(comparison, eParam);

var countMonthly1 = ctx.tblMonthlyInput.Join(ctx.tblEmployee, a => a.CompanyId, b => b.CompanyId, (a, b) => b).Where(lambda).Count();

我想使用linq表达式使上述查询适用于Contains方法

示例查询:

var countMonthly = (from a in ctx.tblMonthlyInput
                    join b in ctx.tblEmployee on a.CompanyId equals b.CompanyId
                    where categoryId.Contains(a.CategoryId)  //want to make this dynamic
                    select a).Count() == 0;

Answer 1

这对你有用:

void Main()
{
    var filterField = "Id";
    List<int> Ids = new List<int>();
    var eParam = Expression.Parameter(typeof(EmployeeDetail), "e");
    var method = Ids.GetType().GetMethod("Contains");
    var call = Expression.Call(Expression.Constant(Ids), method, Expression.Property(eParam, filterField));
    var lambda = Expression.Lambda<Func<EmployeeDetail, bool>>(call, eParam);
}

public class EmployeeDetail
{
    public int Id { get; set; }
}

首先,您Contains在类型上查找方法Ids.然后我们只是Ids作为实例调用它,并将属性作为参数调用