我正在尝试将一些直接构建 SQL 查询的旧代码转换为 Entity Framework,并且遇到了一个许多人似乎都有的问题(从围绕该主题的大量问题来看):如何表达动态 where 条件在 linq 中。
如何使用 linq 查询来表达以下代码:
switch (status) {
case "0":
sqlwhere = " WHERE status < 0 ";
break;
case "-1":
sqlwhere = " WHERE status = -1 ";
break;
case "-100":
sqlwhere = " WHERE status = -100 ";
break;
case "1":
default:
sqlwhere = " WHERE status >= 0 ";
break;
}
if (strsearch != "")
sqlwhere += " AND desc LIKE '%" + strsearch + "%' ";
string sqlc = "SELECT top 10 * FROM c " + sqlwhere + " order by date desc";
我在其他帖子中读到了有关 PredicateBuilder
和动态 Linq 扩展的内容,但我认为像这样的简单案例在没有外部库的情况下也是可以解决的。
使用 .net 4.5、EF 5.0、C#,这是否可以在不为每个案例构建完整的 linq 语句的情况下以“动态”方式完成?
最佳答案
如果您不想使用外部的东西,那么只需使用流畅的 API:
var query = db.YourTableName
.Where(x => x.desc.Contains(strsearch));
switch (status) {
case "0":
query = query.Where(x => x.status < 0);
break;
case "-1":
query = query.Where(x => x.status == -1);
break;
case "-100":
query = query.Where(x => x.status == -100);
break;
case "1":
default:
query = query.Where(x => x.status >= 0);
break;
}
var result = query.OrderByDescending(x => x.date)
.Take(10);
BTW 您可以创建按状态过滤的扩展方法。您的查询将如下所示:
var query = db.YourTableName
.FilterByStatus(status)
.Where(x => x.desc.Contains(strsearch))
.OrderByDescending(x => x.date)
.Take(10);
扩展方法:
public static IQueryable<YourType> FilterByStatus(this IQueryable<YourType> query,
string status)
{
switch (status) {
case "0":
return query.Where(x => x.status < 0);
case "-1":
return query.Where(x => x.status == -1);
case "-100":
return query.Where(x => x.status == -100);
case "1":
default:
return query.Where(x => x.status >= 0);
}
}
关于c# - Linq-to-Entities 查询中的动态条件,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/13233461/