C# 动态构建LINQ到实体Where子句

如何动态构建where子句，有时

OwnerID

将仅为零

itemID

，并且

LocationID

将作为搜索条件提供，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();

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

有时

OwnerID

和

ItemId

将为零，那么只有

LocationID

将作为搜索条件提供，在这种情况下，LINQ应为零

(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();

(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，然后LINQ将如下所示

(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

子句在更改，请帮我解决。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

）。

通过使用基于方法的查询，您可以轻松地做到这一点。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();

---

最简单的方法是检查Where子句中的零条件：

(from s in repository.ItemOwners.Include("OwnerDetails")
where (searchCriteria.OwnerID == 0 || s.OwnerId == searchCriteria.OwnerID) && 
(searchCriteria.ItemID == 0 || s.ItemId == searchCriteria.ItemID) && 
s.OwnerDetails.LocationId == searchCriteria.LocationID
select new { s.OwnerDetails.OwnerName, s.OwnerDetails.MobNumber }).ToList();

---

在这种情况下，这是最具可读性和正确性的方法