mysql - Entity Framework 6 - DbFunctions.AddHours 错误

Question

我有一项任务是在特定时间段内获取一组实体。我正在使用代码优先方法和 MySql 服务器。

代码

IQueryable<Entity> query = dbContext.Set<Entity>().AsNoTracking();

Entity[] entities = (from e in query
               let last = (from ee in query orderby ee.Id descending select ee).FirstOrDefault()
               where e.Timestamp >= DbFunctions.AddHours(last.Timestamp, -hours)
               select e).ToArray();

以及由 EF 6.1.3 生成的以下 SQL

SELECT
`Extent1`.`Id`, 
`Extent1`.`Timestamp`
FROM `Entities` AS `Extent1` LEFT OUTER JOIN (SELECT
`Extent2`.`Id`, 
`Extent2`.`Timestamp`
FROM `Entities` AS `Extent2`
 ORDER BY 
`Extent2`.`Id` DESC LIMIT 1) AS `Limit1` ON 1 = 1
 WHERE `Extent1`.`Timestamp` >= (AddHours(`Limit1`.`Timestamp`, -(@p__linq__0)))

我遇到了一个错误

Failed in 6 ms with error: FUNCTION mydb.AddHours does not exist

事实上，我在数据库端还没有这个功能。有人知道那些 DbFunctions 是如何工作的吗？

UPD

类似问题

EntityFramework 6.1.3 and MySQL DbFunctions.TruncateTime does not exist?

how to use canonical functions in Entity Framework and Mysql

Answer 1

目前的解决方法 - 只是在 DbInitializer 中添加了函数的实现

CREATE FUNCTION AddHours(timeValue datetime, addValue int) RETURNS datetime
        RETURN DATE_ADD(timeValue, INTERVAL addValue HOUR);