从多个谓词构建 IQueryable

Question

我想在过滤器属性具有值（非空）时使用 where 条件构建查询。如果使用多个过滤器，则必须是 AND 组合。

当相应的属性值不为 null 时，combine/add 每个谓词如何才能使最终查询准备好进行过滤？

IQueryable<Customer> filter = null;

Expression<Func<Customer, bool>> predicatetest1 = res => res.test1 == request.test1;
Expression<Func<Customer, bool>> predicatetest2 = res => res.test2 == request.test2;
Expression<Func<Customer, bool>> predicatetest3 = res => res.test3 == request.test3;

if (request.test1 != null)
{
     // add the above predicate to the filter
}

if (request.test2 != null)
{
    // add the above predicate to the filter
}

if (request.test3 != null)
{
   // add the above predicate to the filter
}

Answer 1

IQueryable<Customer> filter = Context.Customers;

if (request.test1 != null)
{
  filter = filter.Where(predicatetest1);
}

if (request.test2 != null)
{
  filter = filter.Where(predicatetest2);
}

if (request.test3 != null)
{
  filter = filter.Where(predicatetest3);
}

var customers = filter.ToList();

当所有 3 个属性都不为 null 时，以下内容是等效的

Context.Customers.Where(predicatetest1).Where(predicatetest2).Where(predicatetest3).ToList();

从多个谓词构建 IQueryable

Build an IQueryable from multiple predicates

linq-to-entities

entity-framework

iqueryable