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AlexLEWIS edited this page Sep 29, 2021 · 13 revisions

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1、导航属性 ManyToOne

ManyToOne 导航属性通过 ToList(includeNestedMembers: false) 加载，参数说明：

false: 返回 2级 Join 的导航数据（默认）；

true: 返回所有层级深度 Join 的导航数据（未使用的导航数据不会返回）；

Select<Tag>().Include(a => a.Parent.Parent).ToList(true);

Select<Tag>().Where(a => a.Parent.Parent.Name == "1").ToList(true);
//这样写，不需要再标记 Join，解析表达式时自动处理成 LeftJoin

2、导航属性 OneToMany/ManyToMany

IncludeMany 贪婪加载集合的导航属性，其实是分两次查询，在 ToList 后进行了数据重装。

Select<Tag>().IncludeMany(a => a.Songs).ToList();

IncludeMany 有第二个参数，可以进行二次查询前的修饰工作。

Select<Tag>().IncludeMany(a => a.Songs, 
    then => then.Where(song => song.User == "admin")).ToList();

In fact, in Then, you can continue to use Include/IncludeMany. As long as you like it, it’s okay to go down 100 levels.

Mutations

It can also be greedily loaded without configuring the navigation relationship.

Select<Tag>().IncludeMany(a => a.TestManys.Where(b => b.TagId == a.Id));

Only query the first few pieces of data in each sub-collection to avoid poor IO performance caused by loading all data like EfCore (for example, there are 2000 comments under a product).

Select<Tag>().IncludeMany(a => a.TestManys.Take(10));

The sub-collection returns a part of the fields to avoid the problem of too many fields.

Select<Tag>().IncludeMany(a => a.TestManys.Select(b => new TestMany { Title = b.Title ... }));

IncludeMany Extensions

When the main data already exists in the memory, how to load the sub-data? So we added the List<T> extension method, the example is as follows:

new List<Song>(new[] { song1, song2, song3 }).IncludeMany(fsql, a => a.Tags);

Comparison of the Two Ways of IncludeMany

Way 1: IncludeMany extensions

var list111 = fsql.Select<SysModule>()
    .Page(1, 10)
    .ToList(a => new { Id = a.Id }) //Query data id
    .Select(a => new SysModule { Id = a.Id }).ToList() //Memory operation
    .IncludeMany(fsql, a => a.Permissions, then => then.Include(a => a.Button));
SELECT a."Id" as1 
FROM "SysModule" a 
limit 0,10

SELECT a."Id", a."SysModuleId", a."SysModuleButtonId", a."Status", 
a__Button."Id" as5, a__Button."Name", a__Button."EventName", a__Button."EnCode", a__Button."Icon", a__Button."Sort", a__Button."CreateTime" 
FROM "SysModulePermission" a 
LEFT JOIN "SysModuleButton" a__Button ON a__Button."Id" = a."SysModuleButtonId" 
WHERE ((a."SysModuleId") in ('menu1','menu2'))

Way 2: Directly IncludeMany + ToList

var list222 = fsql.Select<SysModule>()
    .IncludeMany(m => m.Permissions, then => then.Include(a => a.Button))
    .Page(1, 10)
    .ToList();
SELECT a."Id", a."ParentId", a."Name", a."Icon", a."UrlAddress", a."IsShow", a."Sort", a."Description", a."CreateTime" 
FROM "SysModule" a 
limit 0,10

SELECT a."Id", a."SysModuleId", a."SysModuleButtonId", a."Status", 
a__Button."Id" as5, a__Button."Name", a__Button."EventName", a__Button."EnCode", a__Button."Icon", a__Button."Sort", a__Button."CreateTime" 
FROM "SysModulePermission" a 
LEFT JOIN "SysModuleButton" a__Button ON a__Button."Id" = a."SysModuleButtonId" 
WHERE ((a."SysModuleId") in ('menu1','menu2'))

Case: Query Vod table, 10 data for each of category 1, category 2, and category 3

class Vod {
    public Guid Id { get; set; }
    public int TypeId { get; set; }
}

//Define a temporary class, it can also be a DTO
class Dto {
    public int TypeId { get; set; }
    public List<Vod> Vods { get; set; }
}

var dto = new [] { 1,2,3 }.Select(a => new Dto { TypeId = a }).ToList();
dto.IncludeMany(fsql, d => d.Vods.Take(10).Where(vod => vod.TypeId == d.TypeId));

//After execution, each element.Vods of DTO will only have 10 records

Reference

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