Question

我是实体框架的新手。我需要根据订单和客户开发Linq查询。

for eg：string firstName可以包含三个值中的任何一个

1）null 2）乔 3）喜欢％Joe％'

simailary我需要为姓氏开发

我当前的查询是这样的

using (NorthwindEntities ent = new NorthwindEntities()) { var UsersList = ent.User.Include("Orders"). Include("OrderDetails"). Include("OrderDetails.Products"). .Where(o => (firstName== null || o.firstName== firstName||o.firstName.Contains(firstName)) && (LastName== null || o.LastName== LastName ||o.LastName.contains(LastName) ) }

我的查询是否正确。是否有其他更好的选择来编写linq实体查询。

由于

Answer 1

你可以将你的查询分成几部分，然后它会更好：

var UsersList = ent.User.Include("Orders")
                        .Include("OrderDetails")
                        .Include("OrderDetails.Products");

if(!string.IsNullOrEmpty(firstName));
   UsersList = UsersList.Where( o => o.firstName.Contains(firstName));

if(!string.IsNullOrEmpty(lastName));
   UsersList = UsersList.Where( o => o.lastName.Contains(lastName))

检查o.firstName == firstName也是多余的，Contains(firstName)部分就足够了（对于lastName也一样）。

Answer 2

您可以向Queryable对象添加条件。这些条件将一直存在，直到执行数据查询。

var UsersList = ent.User.Include("Orders")
               .Include("OrderDetails")
               .Include("OrderDetails.Products");

if (!string.IsNullOrEmpty(firstName))
   UsersList = UsersList.Where( o => o.firstName.Contains(firstName));

if (!string.IsNullOrEmpty(LastName))
   UsersList = UsersList.Where( o => o.LastName.Contains(LastName));

Answer 3

您可以按步骤构建查询：

    using (NorthwindEntities ent = new NorthwindEntities())
    {
       var UsersList = ent.User.Include("Orders")
                .Include("OrderDetails")
                .Include("OrderDetails.Products");
       if (LastName != null)
          UserList = UserList.Where(o => o.LastName == LastName || o.LastName.contains(LastName));

       if (FirstName != null)
          UserList = UserList.Where(o => o.firstName== firstName||o.firstName.Contains(firstName);

       // etc
   }

在您执行ToList（）或在foreach或类似的内容中使用它之前，查询将不会执行。

动态where子句实体框架3.5

3 个答案: