c# - 动态构建 LINQ-To-Entities Where 子句

Question

我如何动态构建 where 子句，有时 OwnerID 将为零，只有 itemID 和 LocationID 将作为搜索提供标准，在这种情况下，LINQ 应该是

(from s in repository.ItemOwners.Include("OwnerDetails")
 where s.ItemId == searchCriteria.ItemID && 
       s.OwnerDetails.LocationId == searchCriteria.LocationID
 select new { s.OwnerDetails.OwnerName, s.OwnerDetails.MobNumber }).ToList();

有时 OwnerID 和 ItemId 将为零，然后仅提供 LocationID 作为搜索条件，在这种情况下，LINQ应该是

(from s in repository.ItemOwners.Include("OwnerDetails")
 where s.OwnerDetails.LocationId == searchCriteria.LocationID
 select new { s.OwnerDetails.OwnerName, s.OwnerDetails.MobNumber }).ToList();

有时会提供整个 OwnerID、ItemID 和 LocationID 作为搜索条件，那么 LINQ 会像这样

(from s in repository.ItemOwners.Include("OwnerDetails")
 where s.OwnerId == searchCriteria.OwnerID && 
       s.ItemId == searchCriteria.ItemID && 
       s.OwnerDetails.LocationId == searchCriteria.LocationID
 select new { s.OwnerDetails.OwnerName, s.OwnerDetails.MobNumber }).ToList();

这里只有where子句有变化，请帮我解决。我如何动态构建 where 子句(请注意，这里我有一个导航属性，它是 OwnerDetails.LocationId)。

Answer 1

您可以使用基于方法的查询轻松地做到这一点。您可以一次添加一个条件，并在最后调用 Select 和 ToList:

// Where(x => true) might not be necessary, you can try skipping it.
var query = repository.ItemOwners.Include("OwnerDetails").Where(x => true);

if (searchCriteria.OwnerID != null)
    query = query.Where(s => s.OwnerID == searchCriteria.OwnerID);
if (searchCriteria.ItemID != null)
    query = query.Where(s => s.ItemID == searchCriteria.ItemID);
if (searchCriteria.OwnerID != null)
    query = query.Where(s => s..OwnerDetails.LocationId == searchCriteria.LocationID);

var results = query.Select(s => new { s.OwnerDetails.OwnerName, s.OwnerDetails.MobNumber }).ToList();