EF Code First：添加外鍵關係Linq-to-Entity投影

Question

我在創建數據庫時使用實體框架首先從代碼創建外鍵。查詢下面顯示的表格，並將數據投影到另一個模型中，如下所示。一切似乎都是正確的，儘管當我查詢數據時，由AddressId連接的列似乎不工作，我的「街道」列返回空白數據。

namespace Mvc4Connect.ViewModels 
{ 

[Table("PersonEntity")] 
public class PersonEntity : EntityTypeConfiguration<PersonEntity> 
    { 
    //Constructor 
    public PersonEntity() 
    { 
     this.ToTable("TB008555", schemaName: "SchemaUser"); 
     this.Property(c => c.PersonId).HasColumnName("CL005500"); 
     this.Property(c => c.FirstName).HasColumnName("CL005545"); 
     this.Property(c => c.LastName).HasColumnName("CL005550"); 
     this.Property(c => c.AddressId).HasColumnName("CL044760"); 
    } 


    [Key] 
    [DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)] 
    public int PersonId { get; set; } 
    public String FirstName { get; set; } //firstname 
    public String LastName { get; set; } //lastname 

    [ForeignKey("AddressEntity")] 
    public int AddressId { get; set; } 

    public virtual ICollection<AddressEntity> AddressEntity { get; set; } 
    } 

} 

我包含連接AddressId

namespace Mvc4Connect.ViewModels 
{ 

[Table("AddressEntity")] 
public class AddressEntity : EntityTypeConfiguration<AddressEntity> 
{ 
    //Constructor 
    public AddressEntity() 
    { 

     this.ToTable("TB047697", schemaName: "SchemaUser"); 
     this.Property(c => c.AddressId).HasColumnName("CL045695"); 
     this.Property(c => c.Street).HasColumnName("CL042710"); 
     this.Property(c => c.City).HasColumnName("CL044747"); 
     this.Property(c => c.State).HasColumnName("CL047460"); 
    } 

    [Key] 
    [DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)] 
    public int AddressId { get; set; } 
    public string Street { get; set; }   
    public string City { get; set; } 
    public string State { get; set; } 

} 

} 

我的實體上下文

public class EntityContext : DbContext 
{ 
public DbSet<PersonEntity> Persons { get; set; } 
public DbSet<AddressEntity> Address { get; set; } 

protected override void OnModelCreating(DbModelBuilder modelBuilder) 
{ 
     modelBuilder.Configurations.Add(new PersonEntity()); 
     modelBuilder.Configurations.Add(new AddressEntity()); 
} 
} 

這第二個表是我想在我的API控制器使用查詢。

var dbv = new EntityContext(); 

var query = (from vt in dbv.Persons 
        from ad in dbv.Address 
        where vt.LastName.StartsWith(ln) 
        where vt.FirstName.StartsWith(fn) 
        where ad.AddressId == vt.AddressId 
        select new PersonVM() // Create new object for projection 
        { 
         PersonId = vt.PersonId, 
         FirstName = vt.FirstName, 
         LastName = vt.LastName, 
         Street = ad.Street, // Blank Street data 
         AddressId = vt.AddressId // Debug to assure Id is assigned 
        }); 

     return query.ToList(); 

Answer 1

我認爲，你當確定表之間的關係做出錯誤：組合：

public class PersonEntity : EntityTypeConfiguration<PersonEntity> 
{ 
    [ForeignKey("AddressEntity")] 
    public int AddressId { get; set; }  
    public virtual ICollection<AddressEntity> AddressEntity { get; set; } 
    //other properties... 
} 

不正確！相反的，如果人與地址之間的關係是一個一對多的你應該寫這樣：

public class PersonEntity : EntityTypeConfiguration<PersonEntity> 
{ 
    //[ForeignKey("AddressEntity")] 
    //public int AddressId { get; set; }  
    public virtual ICollection<AddressEntity> AddressEntity { get; set; } 
    //other properties... 
} 

而且

public class AddressEntity : EntityTypeConfiguration<AddressEntity> 
{ 
    [ForeignKey("Person")] 
    public int PersonId { get; set; } 
    public virtual PersonEntity Person { get; set; } 
    //other properties... 
} 

最終的查詢將是這個樣子：

var query = (from vt in dbv.Persons 
      from ad in dbv.Address 
      where vt.LastName.StartsWith(ln) 
      where vt.FirstName.StartsWith(fn) 
      where vt.PersonId == ad.PersonId//this line was changed! 
      select new PersonVM 
      { 
       vt.PersonId, 
       vt.FirstName, 
       vt.LastName, 
       ad.Street, 
       ad.AddressId //this line was changed! 
      }); 

此查詢將返回不是人員，但地址與關於它人的信息。如果你想帶人與他們的地址，你應該執行分組的操作，並且還留下外部連接以保存沒有地址的人：

var query = (from vt in dbv.Persons      
      where vt.LastName.StartsWith(ln) 
      where vt.FirstName.StartsWith(fn) 
      join ad in dbv.Address on vt.PersonId equals ad.PersonId into subAddresses 
      from subAdr in subAddresses.DefaultIfEmpty() 
      group subAdr by new { vt.PersonId, vt.FirstName, vt.LastName } into groupPers           
      select new 
      { 
        groupPers.Key.PersonId, 
        groupPers.Key.FirstName, 
        groupPers.Key.LastName, 
        addresses = groupPers 
       });