如何使用 Dapper 查询具有一对多关系的对象?

How to query an object with one-to-many relationship using Dapper?

我有(显然是简化的)表格,例如:

public class Father
{
    [Key]
    public int Id { get; set; }
    public string Name { get; set; }
    public List<Son> Sons { get; set; } = new List<Son>();
}

public class Son
{
    [Key]
    public int Id { get; set; }
    public int FatherId { get; set; }
    public string Name { get; set; }
}

在数据库中,我有 1 个 ID = 1 的父亲和 3 个 FatherId = 1 的儿子。

我的查询是这样的:

conn.Query<Father, Son, Father>(
    @"SELECT f.*, s.* FROM Father f INNER JOIN Son s ON f.Id = s.FatherId WHERE f.Id = 1", 
    (f, s) => 
    {
        f.Sons.Add(s);
        return f;
    },
);

上面的查询给了我一个 3 个父亲的 IEnumerable,每个父亲包含一个儿子,而不是我想要的:一个父亲对象,儿子 属性 包含 3 个儿子对象。

我可以这样做,但我不确定这是否是最好的方法:

// Get father
var father = await connection.GetAsync<Father>(id);
// Get related sons
var sql = $"SELECT * FROM Son a WHERE a.FatherId = {father.Id}";
var sons = (await connection.QueryAsync<Address>(sql)).AsList();
// Stitch em all together
father.Sons.AddRange(sons);

我想知道这是否是最好的方法。我们如何使用 Dapper 获取包含所有相关对象的单个对象?

有一些方法可以做到这一点,请参阅 How do I write one to many query in Dapper.Net?

我希望按如下方式进行:

var fatherDictionary = new Dictionary<int, Father>();

var list = connection.Query<Father, Son, Father>(
    @"SELECT f.*, s.* FROM Father f INNER JOIN Son s ON f.Id = s.FatherId WHERE f.Id = 1",
    (f, s) =>
    {
        Father fatherEntry;

        if (!fatherDictionary.TryGetValue(f.Id , out fatherEntry))
        {
            fatherEntry = f;
            fatherEntry.Sons = new List<Son>();
            fatherDictionary.Add(fatherEntry.Id, fatherEntry);
        }

        fatherEntry.Sons.Add(s);
        return fatherEntry;
    })
.Distinct()
.ToList();

参见示例:https://dapper-tutorial.net/result-multi-mapping#example-query-multi-mapping-one-to-many