Dapper 从 JOIN 查询中接收列表作为对象参数

Question

当我想从数据库映射我的对象时，我在使用 Dapper 时遇到了问题。

class Set
{
    public Guid Id { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
    public List<Guid> GeneratorsList { get; set; }
}

它包含一个列表，所以我创建了单独的 table 来保存它，就像那样

CREATE TABLE [dbo].[Sets] (
    [Id]          UNIQUEIDENTIFIER NOT NULL,
    [Name]        VARCHAR (60)     NOT NULL,
    [Description] VARCHAR (60)     NULL,
    PRIMARY KEY CLUSTERED ([Id] ASC)
);

CREATE TABLE [dbo].[Set_Generator] (
    [SetId]       UNIQUEIDENTIFIER NOT NULL,
    [GeneratorId] UNIQUEIDENTIFIER NOT NULL,
    PRIMARY KEY CLUSTERED ([SetId] ASC, [GeneratorId] ASC),
    FOREIGN KEY ([SetId]) REFERENCES [dbo].[Sets] ([Id]) ON DELETE CASCADE
);

我想从那些 table 中检索正确的 Set 对象，代码工作量最少。我尝试加入它们并将结果强类型输入 Set，但没有成功。

var result = conn.Query<Set>(@"SELECT [S].[Id], [S].[Name], [S].[Description], [SG].[GeneratorId] AS [GeneratorsList] FROM [Sets] AS [S] INNER JOIN [Set_Generator] AS [SG] ON [S].[Id] = [SG].[SetId];");

我知道我可以简单地从 table 中检索 Set，然后从单独的查询中添加 GeneratorsList，但我正在寻找更好的解决方案。

var sets = conn.Query<Set>(@"SELECT * FROM [Sets];");
foreach(var set in sets)
{
    var generators = conn.Query<Guid>(@"SELECT [GeneratorId] FROM [Set_Generator] WHERE [SetId]=@SetId", new { SetId = set.Id });
    set.GeneratorsList = generators.ToList();
}

是否有只需要一次查询的解决方案？

Answer 1

使用您提供的查询，您可能会收到：

internal class GeneratorSet
{
    public Guid Id { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
    public Guid GeneratorId { get; set; }
}

并使用linq GroupBy构造Set对象(-s):

var generatorSets = conn.Query<GeneratorSet>(@"SELECT [S].[Id], [S].[Name], [S].[Description], [SG].[GeneratorId] AS [GeneratorsList] FROM [Sets] AS [S] INNER JOIN [Set_Generator] AS [SG] ON [S].[Id] = [SG].[SetId];");;

var res = generatorSets.GroupBy(gen => gen.Id, p => p, (key, g) => new Set()
      { Id = key, Generators = g.Select(g => g.GeneratorId)});

Dapper 从 JOIN 查询中接收列表作为对象参数

Dapper receive List as object parameter from JOIN query

c#

sql-server

dapper