ServiceStack ORMLite：带有表别名的多列 GroupBy答案

【问题标题】：ServiceStack ORMLite: Mutliple Column GroupBy With Table AliasesServiceStack ORMLite：带有表别名的多列 GroupBy
【发布时间】：2020-02-11 16:54:36
【问题描述】：

我希望使用 ORMLite 按多个别名表进行分组，但我似乎遇到了问题。

当在 SqlExpression 的 GroupBy 中使用带有匿名类型的 Sql.TableAlias 时，为 group by 生成的 SQL 包含来自匿名类型的属性名称（即 AliasName."Column" As PropertyName）。

下面的代码可以重现这个问题：

public class Thing
{
    public int? Id { get; set; }
}

public class Stuff
{
    public int? Id { get; set; }
    public int? ThingId { get; set; }
    public int? Type { get; set;  }
}

string brokenGroupBy = db
    .From<Thing>()
    .Join<Stuff>((thing, stuff) => stuff.ThingId == thing.Id && stuff.Type == 1, db.TableAlias("StuffTypeOne"))
    .Join<Stuff>((thing, stuff) => stuff.ThingId == thing.Id && stuff.Type == 2, db.TableAlias("StuffTypeTwo"))
    .GroupBy<Thing, Stuff>((thing, stuff) => new
    {
        ThingId = thing.Id,
        StuffTypeOneId = Sql.TableAlias(stuff.Id, "StuffTypeOne"),
        StuffTypeTwoId = Sql.TableAlias(stuff.Id, "StuffTypeTwo")
    })
    .Select<Thing, Stuff>((thing, stuff) => new
    {
        ThingId = thing.Id,
        StuffTypeOneId = Sql.TableAlias(stuff.Id, "StuffTypeOne"),
        StuffTypeTwoId = Sql.TableAlias(stuff.Id, "StuffTypeTwo")
    })
    .ToMergedParamsSelectStatement();

brokenGroupBy字符串中生成并存储的SQL如下：

SELECT "thing"."id"      AS "ThingId", 
       StuffTypeOne."id" AS StuffTypeOneId, 
       StuffTypeTwo."id" AS StuffTypeTwoId 
FROM   "thing" 
       INNER JOIN "stuff" "StuffTypeOne" 
               ON ( ( "StuffTypeOne"."thingid" = "thing"."id" ) 
                    AND ( "StuffTypeOne"."type" = 1 ) ) 
       INNER JOIN "stuff" "StuffTypeTwo" 
               ON ( ( "StuffTypeTwo"."thingid" = "thing"."id" ) 
                    AND ( "StuffTypeTwo"."type" = 2 ) ) 
GROUP  BY "thing"."id", 
          StuffTypeOne."id" AS stufftypeoneid, 
          StuffTypeTwo."id" AS stufftypetwoid

在这种情况下是否不支持表别名，或者在这种情况下是否有不同的方式来指定分组依据？

我已经使用 group by 中的自定义 SQL 表达式实现了我想要的结果，但我更喜欢不需要 SQL 字符串的解决方案。

【问题讨论】：

标签： ormlite-servicestack

【解决方案1】：

我已经从 v5.8.1 发布了对 OrmLite 的更新，现在是 available on MyGet，它还将从 Group By Expressions 中删除别名，以便您的 group by 表达式：

.GroupBy<Thing, Stuff>((thing, stuff) => new
{
    ThingId = thing.Id,
    StuffTypeOneId = Sql.TableAlias(stuff.Id, "StuffTypeOne"),
    StuffTypeTwoId = Sql.TableAlias(stuff.Id, "StuffTypeTwo")
})

现在应该生成类似：

thing.Id, "StuffTypeOne"."Id", "StuffTypeTwo"."Id"

虽然您已经在 SELECT 表达式中定义了别名，但您可以重用它们：

.GroupBy<Thing, Stuff>((thing, stuff) => new
{
    ThingId = thing.Id,
    StuffTypeOneId = "StuffTypeOneId",
    StuffTypeTwoId = "StuffTypeTwoId"
})

或者您可以使用对象数组来实现更简洁的表达式：

.GroupBy<Thing, Stuff>((thing, stuff) => new object[]
{
    thing.Id,
    "StuffTypeOneId",
    "StuffTypeTwoId"
})

【讨论】：