将来自 JSON 数组对象字段的数据与另一个表连接起来

Question

假设，我在 Postgre 数据库中有两个表，如下所示：

CREATE TABLE "MST"."Users" (
  "Id" uuid NOT NULL DEFAULT uuid_generate_v4(),
  "Uid" varchar(32) COLLATE "pg_catalog"."default" NOT NULL,
  "Pid" varchar(100) COLLATE "pg_catalog"."default" NOT NULL,
  "Details" jsonb,
  "Contacts" jsonb,
  "Trackers" jsonb NOT NULL,
  "Configurations" jsonb,
  PRIMARY KEY ("Id"),
  UNIQUE ("Uid")
);

CREATE TABLE "MST"."Teams" (
  "Id" uuid NOT NULL DEFAULT uuid_generate_v4(),
  "Details" jsonb NOT NULL,
  "Members" jsonb,
  "Trackers" jsonb NOT NULL,
  PRIMARY KEY ("Id")
);

这两个表都映射到以下模型：

    [Table("Users", Schema = "MST")]
    public partial class Users
    {
        [Key]
        public Guid Id { get; set; }
        
        [Required]
        [StringLength(32)]
        public string Uid { get; set; }
        
        [Required]
        [StringLength(100)]
        public string Pid { get; set; }

        [Column(TypeName = "jsonb")]
        public UserDetailsModel Details { get; set; }

        [Column(TypeName = "jsonb")]
        public UserContactsModel Contacts { get; set; }

        [Required]
        [Column(TypeName = "jsonb")]
        public TrackersModel Trackers { get; set; }

        [Column(TypeName = "jsonb")]
        public UserConfigurationsModel Configurations { get; set; }
    }

    [Table("Teams", Schema = "MST")]
    public partial class Teams
    {
        [Key]
        public Guid Id { get; set; }

        [Required]
        [Column(TypeName = "jsonb")]
        public TeamDetailsModel Details { get; set; }
        
        [Column(TypeName = "jsonb")]
        public List<TeamMembersModel> Members { get; set; }

        [Required]
        [Column(TypeName = "jsonb")]
        public TrackersModel Trackers { get; set; }
    }

    // Childs classes
    public class TeamMembersModel
    {
        [Required(ErrorMessage = @"Member ""User ID"" is required and can not be empty.")]
        [StringLength(maximumLength: 32, MinimumLength = 3, ErrorMessage = @"Member ""User ID"" length must be between 3 and 32 chars.")]
        public string Uid { get; set; }

        public bool IsLead { get; set; } = false;

        public UserDetailsModel Details { get; set; }
    }

    public UserContactModel { 
        ...some properties...
    }

    public TrackersModel { 
        ...some properties...
    }

    public UserDetailsModel { 
        ...some properties...
    }

以下是Teams表中的数据样本：

INSERT INTO "MST"."Teams"("Id", "Details", "Members", "Trackers") VALUES ('daf0e3d3-78bf-443b-8b0b-6f74d2eabd7f', '{"Name": "My First Team", "Files": [], "Notes": null, "Photo": null}', '[{"Uid": "fadhly.permata", "IsLead": true}, {"Uid": "humaira.permata", "IsLead": false}]', '{"Status": "RG", "Created": {"At": "2020-08-14T12:15:59.4175028+00:00", "By": "SYSTEM"}, "Updated": null}');

INSERT INTO "MST"."Teams"("Id", "Details", "Members", "Trackers") VALUES ('538f1d58-01cb-4120-b89a-ea25bfacaa25', '{"Name": "My Second Team", "Files": [], "Notes": null, "Photo": null}', '[{"Uid": "fadhly.permata", "IsLead": true, "Details": null}]', '{"Status": "RG", "Created": {"At": "2020-08-19T10:51:44.5128139+00:00", "By": "fadhly.permata"}, "Updated": null}');

正如您在我的数据库数据中看到的，Members 字段与 JSON 数组一起存储。我对如何加入 Teams->Members->Details 和用户表中的详细信息感到困惑。

这是我的查询：

from
    team in _manager.DbContext.Teams

where
    team.Trackers.Status != "DE"

orderby
    team.Details.Name

select
    new Models.Teams
    {
        Id = team.Id,
        Details = team.Details,
        Trackers = team.Trackers,
        Members = team.Members.Select(
            x => new TeamMembersModel { 
                Uid = x.Uid, 
                IsLead = x.IsLead, 
                Details = _manager.DbContext.Users.First(y => y.Uid == x.Uid).Details 
            }
        )
            .ToList()
    };

但我对上述查询没有运气，并收到以下错误消息： "Object reference not set to an instance of an object."

也许，我遗漏了一些东西，但不确定它在哪里。

---

注意： 我正在使用 NPGSQL 作为 EF 引擎的附加/扩展，因为我也在这个问题标签上添加了。

Answer 1

问题在于您对team.Members 的投影，这是一个 JSON 属性而不是 EF 导航 - 这无法转换为 SQL 以便在 PostgreSQL 中进行处理。由于这是最终的预测，这应该简单地得到客户评估，但 EF 似乎有一个关于此的错误（打开 https://github.com/dotnet/efcore/issues/22161 进行跟踪）。

如果目的是让客户评估，只需在投影之前放置一个 AsEnumerable - 这应该会使错误消失。否则，

理论上，这可以通过将 JSON 数组投影转换为 json_array_elements (see PG docs) 来完成，但提供者极不可能很快做到这一点。