设置非常简单。端点和部署这两个表是多对多的，并由一个名为“服务”的表连接起来。
var query = from endpoint in db.Endpoints
from deployment in endpoint.Service.Deployments
select new Endpoint(
deployment.Host,
endpoint.Method,
endpoint.Path,
new Cost(endpoint.CostCredits, new PerRequest()));
var result = await query.ToListAsync();
当我运行这个时，我得到 0 个结果。
在调试器中检查 db.Endpoints[0].Service 显示 null。从稍微不同的角度来看:
var query = db.Endpoints
.Include(endpoint => endpoint.Service)
.ThenInclude(s => s.Deployments) // out of desperation!
.SelectMany(endpoint => endpoint.Service.Deployments.Select(deployment =>
new Endpoint(
deployment.Host,
endpoint.Method,
endpoint.Path,
new Cost(endpoint.CostCredits, new PerRequest()))));
这会引发 NullReferenceException。我什至尝试在查询之前添加此内容:
await db.Endpoints.ToListAsync();
await db.Deployments.ToListAsync();
await db.Services.ToListAsync();
相同的行为。
我见过很多这样的问题，例如 EF Core returns null relations until direct access但显然它们不是我的情况 - 即使加载所有三个表中的所有数据后，导航属性也不会填充。
如何让上述查询起作用？
这是一个完整的最小重现(与可运行的 Dotnetfiddle 相同):
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Migrations;
using Microsoft.EntityFrameworkCore.Infrastructure;
using Microsoft.EntityFrameworkCore.Metadata;
namespace Repro
{
class Program
{
static async Task Main()
{
var db = new MorpherDbContext();
db.AddSomeData();
var query = from endpoint in db.Endpoints
from deployment in endpoint.Service.Deployments
select new {
deployment.Host,
endpoint.Method,
endpoint.Path
};
var result = await query.ToListAsync();
Console.WriteLine(result.Count);
}
}
public class Deployment
{
public int Id { get; set; }
public virtual Service Service { get; set; }
public int ServiceId { get; set; }
public string Host { get; set; }
public short? Port { get; set; }
public string BasePath { get; set; }
}
public class Service
{
public int Id { get; set; }
public string Name { get; set; }
public string UrlSlug { get; set; }
public virtual ICollection<Endpoint> Endpoints { get; set; }
public virtual ICollection<Deployment> Deployments { get; set; }
}
public class Endpoint
{
public int Id { get; set; }
public virtual Service Service { get; set; }
public int ServiceId { get; set; }
public string Path { get; set; }
public string Method { get; set; }
public int CostCredits { get; set; }
public string CostType { get; set; }
public string CostTypeParameter { get; set; }
}
public partial class MorpherDbContext : DbContext
{
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
optionsBuilder.UseInMemoryDatabase("db1");
//optionsBuilder.UseSqlServer("Server=(localdb)\\mssqllocaldb;Database=ReproDb;Trusted_Connection=True;MultipleActiveResultSets=true");
base.OnConfiguring(optionsBuilder);
}
public virtual DbSet<Endpoint> Endpoints { get; set; }
public virtual DbSet<Deployment> Deployments { get; set; }
public virtual DbSet<Service> Services { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.HasAnnotation("Relational:DefaultSchema", "dbo");
modelBuilder.Entity<Deployment>(entity =>
{
entity.Property(e => e.Host).IsRequired().HasMaxLength(256);
entity.Property(e => e.BasePath).HasMaxLength(512);
entity.HasOne(deployment => deployment.Service)
.WithMany(service => service.Deployments)
.HasForeignKey(d => d.ServiceId)
.OnDelete(DeleteBehavior.Restrict)
.HasConstraintName("FK_Deployments_Services");
});
modelBuilder.Entity<Service>(entity =>
{
entity.Property(e => e.Name).IsRequired().HasMaxLength(256);
entity.Property(e => e.UrlSlug).IsRequired().HasMaxLength(256);
});
modelBuilder.Entity<Endpoint>(endpoint =>
{
endpoint.Property(e => e.Path).IsRequired();
endpoint.Property(e => e.Method).IsRequired().HasMaxLength(6);
endpoint.Property(e => e.CostCredits).IsRequired();
endpoint.Property(e => e.CostType).IsRequired().HasMaxLength(50);
endpoint.Property(e => e.CostTypeParameter).IsRequired().HasMaxLength(150);
endpoint.HasOne(e => e.Service)
.WithMany(service => service.Endpoints)
.HasForeignKey(e => e.ServiceId)
.OnDelete(DeleteBehavior.Restrict)
.HasConstraintName("FK_Endpoints_Services");
});
OnModelCreatingPartial(modelBuilder);
}
partial void OnModelCreatingPartial(ModelBuilder modelBuilder);
public void AddSomeData()
{
var ws3 = new Service { Name = "Веб-сервис «Морфер»", UrlSlug = "ws"};
Services.Add(ws3);
Deployments.Add(new Deployment {Service = ws3, Host = "ws3.morpher.ru"});
Endpoints.AddRange(new []
{
new Endpoint {Method = "GET", Path = "russian/declension", CostCredits = 1, CostType = "PerRequest"},
new Endpoint {Method = "POST", Path = "russian/declension", CostCredits = 1, CostType = "PerBodyLine"},
new Endpoint {Method = "*", Path = "russian/userdict", CostCredits = 1, CostType = "PerRequest"},
});
ws3.Endpoints = Endpoints.ToList();
SaveChanges();
}
}
}
namespace Repro.Migrations
{
public partial class InitialCreate : Migration
{
protected override void Up(MigrationBuilder migrationBuilder)
{
migrationBuilder.EnsureSchema(
name: "dbo");
migrationBuilder.CreateTable(
name: "Services",
schema: "dbo",
columns: table => new
{
Id = table.Column<int>(nullable: false)
.Annotation("SqlServer:Identity", "1, 1"),
Name = table.Column<string>(maxLength: 256, nullable: false),
UrlSlug = table.Column<string>(maxLength: 256, nullable: false)
},
constraints: table =>
{
table.PrimaryKey("PK_Services", x => x.Id);
});
migrationBuilder.CreateTable(
name: "Deployments",
schema: "dbo",
columns: table => new
{
Id = table.Column<int>(nullable: false)
.Annotation("SqlServer:Identity", "1, 1"),
ServiceId = table.Column<int>(nullable: false),
Host = table.Column<string>(maxLength: 256, nullable: false),
Port = table.Column<short>(nullable: true),
BasePath = table.Column<string>(maxLength: 512, nullable: true)
},
constraints: table =>
{
table.PrimaryKey("PK_Deployments", x => x.Id);
table.ForeignKey(
name: "FK_Deployments_Services",
column: x => x.ServiceId,
principalSchema: "dbo",
principalTable: "Services",
principalColumn: "Id",
onDelete: ReferentialAction.Restrict);
});
migrationBuilder.CreateTable(
name: "Endpoints",
schema: "dbo",
columns: table => new
{
Id = table.Column<int>(nullable: false)
.Annotation("SqlServer:Identity", "1, 1"),
ServiceId = table.Column<int>(nullable: false),
Path = table.Column<string>(nullable: false),
Method = table.Column<string>(maxLength: 6, nullable: false),
CostCredits = table.Column<int>(nullable: false),
CostType = table.Column<string>(maxLength: 50, nullable: false),
CostTypeParameter = table.Column<string>(maxLength: 150, nullable: false)
},
constraints: table =>
{
table.PrimaryKey("PK_Endpoints", x => x.Id);
table.ForeignKey(
name: "FK_Endpoints_Services",
column: x => x.ServiceId,
principalSchema: "dbo",
principalTable: "Services",
principalColumn: "Id",
onDelete: ReferentialAction.Restrict);
});
migrationBuilder.CreateIndex(
name: "IX_Deployments_ServiceId",
schema: "dbo",
table: "Deployments",
column: "ServiceId");
migrationBuilder.CreateIndex(
name: "IX_Endpoints_ServiceId",
schema: "dbo",
table: "Endpoints",
column: "ServiceId");
}
protected override void Down(MigrationBuilder migrationBuilder)
{
migrationBuilder.DropTable(
name: "Deployments",
schema: "dbo");
migrationBuilder.DropTable(
name: "Endpoints",
schema: "dbo");
migrationBuilder.DropTable(
name: "Services",
schema: "dbo");
}
}
}
namespace Repro.Migrations
{
[DbContext(typeof(MorpherDbContext))]
partial class MorpherDbContextModelSnapshot : ModelSnapshot
{
protected override void BuildModel(ModelBuilder modelBuilder)
{
#pragma warning disable 612, 618
modelBuilder
.HasDefaultSchema("dbo")
.HasAnnotation("ProductVersion", "3.1.3")
.HasAnnotation("Relational:MaxIdentifierLength", 128)
.HasAnnotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn);
modelBuilder.Entity("Repro.Deployment", b =>
{
b.Property<int>("Id")
.ValueGeneratedOnAdd()
.HasColumnType("int")
.HasAnnotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn);
b.Property<string>("BasePath")
.HasColumnType("nvarchar(512)")
.HasMaxLength(512);
b.Property<string>("Host")
.IsRequired()
.HasColumnType("nvarchar(256)")
.HasMaxLength(256);
b.Property<short?>("Port")
.HasColumnType("smallint");
b.Property<int>("ServiceId")
.HasColumnType("int");
b.HasKey("Id");
b.HasIndex("ServiceId");
b.ToTable("Deployments");
});
modelBuilder.Entity("Repro.Endpoint", b =>
{
b.Property<int>("Id")
.ValueGeneratedOnAdd()
.HasColumnType("int")
.HasAnnotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn);
b.Property<int>("CostCredits")
.HasColumnType("int");
b.Property<string>("CostType")
.IsRequired()
.HasColumnType("nvarchar(50)")
.HasMaxLength(50);
b.Property<string>("CostTypeParameter")
.IsRequired()
.HasColumnType("nvarchar(150)")
.HasMaxLength(150);
b.Property<string>("Method")
.IsRequired()
.HasColumnType("nvarchar(6)")
.HasMaxLength(6);
b.Property<string>("Path")
.IsRequired()
.HasColumnType("nvarchar(max)");
b.Property<int>("ServiceId")
.HasColumnType("int");
b.HasKey("Id");
b.HasIndex("ServiceId");
b.ToTable("Endpoints");
});
modelBuilder.Entity("Repro.Service", b =>
{
b.Property<int>("Id")
.ValueGeneratedOnAdd()
.HasColumnType("int")
.HasAnnotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn);
b.Property<string>("Name")
.IsRequired()
.HasColumnType("nvarchar(256)")
.HasMaxLength(256);
b.Property<string>("UrlSlug")
.IsRequired()
.HasColumnType("nvarchar(256)")
.HasMaxLength(256);
b.HasKey("Id");
b.ToTable("Services");
});
modelBuilder.Entity("Repro.Deployment", b =>
{
b.HasOne("Repro.Service", "Service")
.WithMany("Deployments")
.HasForeignKey("ServiceId")
.HasConstraintName("FK_Deployments_Services")
.OnDelete(DeleteBehavior.Restrict)
.IsRequired();
});
modelBuilder.Entity("Repro.Endpoint", b =>
{
b.HasOne("Repro.Service", "Service")
.WithMany("Endpoints")
.HasForeignKey("ServiceId")
.HasConstraintName("FK_Endpoints_Services")
.OnDelete(DeleteBehavior.Restrict)
.IsRequired();
});
#pragma warning restore 612, 618
}
}
}
最佳答案
问题在于以下行:
ws3.Endpoints = Endpoints.ToList();
这一行会弄乱 Entity Framework 当前上下文维护的导航属性/集合。事实上，当您尝试在 AddSomeData() 方法中为 Endpoint 对象设置 Service = ws3 时，您将收到以下异常消息:
The association between entities 'Service' and 'Endpoint' with the key value '{ServiceId: 1}' has been severed but the relationship is either marked as 'Required' or is implicitly required because the foreign key is not nullable. If the dependent/child entity should be deleted when a required relationship is severed, then setup the relationship to use cascade deletes.
您正在通过 Add()/AddRange() 方法添加 Endpoint 对象，但没有分配任何 Service 引用(或 ServiceId 值集)。与上面的行结合起来它会中断(以某种方式)。
要解决此问题，您应该删除 ws3.Endpoints = Endpoints.ToList() 行并设置 Service 导航属性，或者删除 Add( )/AddRange() 调用 Endpoint 对象。 AddSomeData() 方法可能如下所示:
public void AddSomeData()
{
var ws3 = new Service { Name = "Веб-сервис «Морфер»", UrlSlug = "ws"};
Services.Add(ws3);
Deployments.Add(new Deployment {Service = ws3, Host = "ws3.morpher.ru"});
var endpointsToAdd = new []
{
new Endpoint {Method = "GET", Path = "russian/declension", CostCredits = 1, CostType = "PerRequest"},
new Endpoint {Method = "POST", Path = "russian/declension", CostCredits = 1, CostType = "PerBodyLine"},
new Endpoint {Method = "*", Path = "russian/userdict", CostCredits = 1, CostType = "PerRequest"},
};
ws3.Endpoints = endpointsToAdd.ToList();
SaveChanges();
}
另一个解决方案是:
public void AddSomeData()
{
var ws3 = new Service { Name = "Веб-сервис «Морфер»", UrlSlug = "ws"};
Services.Add(ws3);
Deployments.Add(new Deployment {Service = ws3, Host = "ws3.morpher.ru"});
Endpoints.Add(new Endpoint {Service = ws3, Method = "GET", Path = "russian/declension", CostCredits = 1, CostType = "PerRequest"});
Endpoints.Add(new Endpoint {Service = ws3, Method = "POST", Path = "russian/declension", CostCredits = 1, CostType = "PerBodyLine"});
Endpoints.Add(new Endpoint {Service = ws3, Method = "*", Path = "russian/userdict", CostCredits = 1, CostType = "PerRequest"});
SaveChanges();
}
关于c# - EF Core 导航属性未填充(再次!)，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/62377299/