C# lambda GroupJoin 但按另一列分组

Question

所以，我正在用 ASP.NET Entity Framework 制作一个小程序。这些是相关模型：

public class Tops
{
    public Tops()
    {
        Dresses = new HashSet<Dresses>();
    }

    [Key] public int id { get; set; }
    public string name { get; set; }
    public int material { get; set; }
    public int meter { get; set; }

    public Inventory materialNavigation { get; set; }
    public Parts_material PartNavigation { get; set; }

    public ICollection<Dresses> Dresses { get; set; }
}

public class Parts_material
{
    public Parts_material()
    {
        Tops = new HashSet<Tops>();
        Sleeves = new HashSet<Sleeves>();
        Patterns = new HashSet<Patterns>();
    }

    public int part_id { get; set; }
    public int material_id { get; set; }

    public Material MaterialNavigation { get; set; }

    public ICollection<Tops> Tops { get; set; }
    public ICollection<Sleeves> Sleeves { get; set; }
    public ICollection<Patterns> Patterns { get; set; }
}

public class Material
{
    public Material()
    {
        Parts_Materials = new HashSet<Parts_material>();
        Inventories = new HashSet<Inventory>();
    }

    public int material_id { get; set; }
    public string material_name { get; set; }

    public ICollection<Parts_material> Parts_Materials { get; set; }
    public ICollection<Inventory> Inventories { get; set; }

}

如您所见，Tops 和 Material 之间存在多对多的关系。如果我想创建一个新的 Top，我想 select 使用 SelectList 的材料。到目前为止，我的 lambda 查询是这样的：

var parts_Materials = _context.Parts_Material.GroupJoin(_context.Materials,
                                                        parts => parts.material_id,
                                                        material => material.material_id,
                                                        (parts, material) => new { Parts_material = parts.part_id, Material = material })
                                             .Select(e => new {
                                                 material_code = e.Material.Select(a => a.material_id),
                                                 material_name = String.Join(", ", e.Material.Select(a => a.material_name))
                                             })
                                             .ToList();

ViewData["material"] = new SelectList(parts_Materials, "material_code", "material_name");

问题是，如果我没有理解错的话，它会按 Parts_material.material_id 分组，但我希望它按 Parts_material.part_id 分组。我已经为此苦苦挣扎了几天，所以我希望有人能帮助我。

Answer 1

已更新 因为 Tops.material 实际上是 Parts_material.part_id.

来自评论的示例数据的预期输出：

<select name="part">
    <option value="1">Kant</option>
    <option value="2">Kant, Jersey</option>
</select>

加入后需要单独分组，不能一次性加入

ViewData["part"] = new SelectList( from pm in _context.Parts_Material join m in _context.Materials on pm.material_id equals m.material_id group m.material_name by pm.part_id into names select new { part_id = names.Key, material_name = string.Join(", ", names) } , "part_id", "material_name");

group 行表示按部件 ID 将 material 名称分组为 IGrouping<>，将部件 ID 映射到 IEnumerable<> 个 material 名称。然后将每个组扁平化为匿名类型，其值和文本内容为 <option>.

我建议您将 material 重命名为 part 以避免将来混淆。

C# lambda GroupJoin 但按另一列分组

C# lambda GroupJoin but Group by another column

c#

asp.net

lambda

many-to-many

selectlist