C＃-首先使用实体​​框架代码，延迟加载无法正常工作

分类：编程问答

如何解决C＃-首先使用实体​​框架代码，延迟加载无法正常工作

我在使用SQL Server数据库的Entity Framework 6代码优先方面遇到一些问题。 我有一个现有的数据库，并且想与Entity Framework一起使用。在Visual Studio 2017中，我添加了ADO.NET实体数据模型类型的新项，以首次生成代码优先类。

一旦生成了类，我就开始使用对象与数据库进行交互。在这里，我有一些关于延迟加载的问题。某些导航属性为null。导航属性标记为virtual，并且延迟加载和ProxyCreationEnabled为true。

这些屏幕截图说明了问题所在：

Navigation Properties at null.

Record in database

Relationships between tables

我可以共享Visual Studio生成的类：

public partial class ETRFContext : DbContext
{
    static string conn = "My connection string";

    public ETRFContext() : base(conn)
    {
    }

    public virtual DbSet<Acessos> Acessos { get; set; }
    public virtual DbSet<Caracteristicas> Caracteristicas { get; set; }
    public virtual DbSet<CircuitoAprovacoes> CircuitoAprovacoes { get; set; }
    public virtual DbSet<EstadosEstudo> EstadosEstudo { get; set; }
    public virtual DbSet<Estudos> Estudos { get; set; }
    public virtual DbSet<GruposAcesso> GruposAcesso { get; set; }
    public virtual DbSet<HistoricoDetalhadoEstudo> HistoricoDetalhadoEstudo { get; set; }
    public virtual DbSet<MembrosGruposAcesso> MembrosGruposAcesso { get; set; }
    public virtual DbSet<Normas> Normas { get; set; }
    public virtual DbSet<Paises> Paises { get; set; }
    public virtual DbSet<PrecedenciasEstudos> PrecedenciasEstudos { get; set; }
    public virtual DbSet<PrecedenciasProgramas> PrecedenciasProgramas { get; set; }
    public virtual DbSet<Programas> Programas { get; set; }
    public virtual DbSet<Projetos> Projetos { get; set; }
    public virtual DbSet<RegistosCAD> RegistosCAD { get; set; }
    public virtual DbSet<TiposEstadoEstudo> TiposEstadoEstudo { get; set; }
    public virtual DbSet<TiposMensagem> TiposMensagem { get; set; }
    public virtual DbSet<TiposProjeto> TiposProjeto { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Caracteristicas>()
            .Property(e => e.Chave)
            .IsFixedLength();

        modelBuilder.Entity<Caracteristicas>()
            .Property(e => e.Valor)
            .IsFixedLength();

        modelBuilder.Entity<Estudos>()
            .HasMany(e => e.EstadosEstudo)
            .WithRequired(e => e.Estudos)
            .HasForeignKey(e => e.idEstudo);

        modelBuilder.Entity<Estudos>()
            .HasMany(e => e.HistoricoDetalhadoEstudo)
            .WithRequired(e => e.Estudos)
            .HasForeignKey(e => e.idEstudo);

        modelBuilder.Entity<Estudos>()
            .HasMany(e => e.PrecedenciasEstudos)
            .WithRequired(e => e.Estudos)
            .HasForeignKey(e => e.idEstudo);

        modelBuilder.Entity<Estudos>()
            .HasMany(e => e.PrecedenciasEstudos1)
            .WithRequired(e => e.Estudos1)
            .HasForeignKey(e => e.idEstudoPrecedencia)
            .WillCascadeOnDelete(false);

        modelBuilder.Entity<Estudos>()
            .HasMany(e => e.RegistosCAD)
            .WithRequired(e => e.Estudos)
            .HasForeignKey(e => e.idEstudo);

        modelBuilder.Entity<GruposAcesso>()
            .HasMany(e => e.Acessos)
            .WithRequired(e => e.GruposAcesso)
            .HasForeignKey(e => e.idGruposAcesso);

        modelBuilder.Entity<GruposAcesso>()
            .HasMany(e => e.MembrosGruposAcesso)
            .WithRequired(e => e.GruposAcesso)
            .HasForeignKey(e => e.idGrupoAcesso);

        modelBuilder.Entity<Paises>()
            .HasMany(e => e.Projetos)
            .WithOptional(e => e.Paises)
            .HasForeignKey(e => e.id_Pais);

        modelBuilder.Entity<Programas>()
            .HasMany(e => e.Acessos)
            .WithRequired(e => e.Programas)
            .HasForeignKey(e => e.idPrograma);

        modelBuilder.Entity<Programas>()
            .HasMany(e => e.CircuitoAprovacoes)
            .WithRequired(e => e.Programas)
            .HasForeignKey(e => e.idPrograma);

        modelBuilder.Entity<Programas>()
            .HasMany(e => e.Estudos)
            .WithRequired(e => e.Programas)
            .HasForeignKey(e => e.idProgramas);

        modelBuilder.Entity<Programas>()
            .HasMany(e => e.PrecedenciasProgramas)
            .WithRequired(e => e.Programas)
            .HasForeignKey(e => e.idProgramaPrecedencia);

        modelBuilder.Entity<Programas>()
            .HasMany(e => e.PrecedenciasProgramas1)
            .WithRequired(e => e.Programas1)
            .HasForeignKey(e => e.idPrograma)
            .WillCascadeOnDelete(false);

        modelBuilder.Entity<Projetos>()
            .HasMany(e => e.Caracteristicas)
            .WithRequired(e => e.Projetos)
            .HasForeignKey(e => e.id_projeto);

        modelBuilder.Entity<Projetos>()
            .HasMany(e => e.Estudos)
            .WithRequired(e => e.Projetos)
            .HasForeignKey(e => e.idProjetos);

        modelBuilder.Entity<TiposEstadoEstudo>()
            .HasMany(e => e.EstadosEstudo)
            .WithRequired(e => e.TiposEstadoEstudo)
            .HasForeignKey(e => e.idEstado);

        modelBuilder.Entity<TiposMensagem>()
            .HasMany(e => e.HistoricoDetalhadoEstudo)
            .WithRequired(e => e.TiposMensagem)
            .HasForeignKey(e => e.idTipoMensagem);

        modelBuilder.Entity<TiposProjeto>()
            .HasMany(e => e.Programas)
            .WithRequired(e => e.TiposProjeto)
            .HasForeignKey(e => e.idTiposProjeto);

        modelBuilder.Entity<TiposProjeto>()
            .HasMany(e => e.Projetos)
            .WithRequired(e => e.TiposProjeto)
            .HasForeignKey(e => e.id_Tipo)
            .WillCascadeOnDelete(false);
    }
}

现在这是类Estudos：

public partial class Estudos
{
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage","CA2214:DoNotCallOverridableMethodsInConstructors")]
    public Estudos()
    {
        EstadosEstudo = new HashSet<EstadosEstudo>();
        HistoricoDetalhadoEstudo = new HashSet<HistoricoDetalhadoEstudo>();
        PrecedenciasEstudos = new HashSet<PrecedenciasEstudos>();
        PrecedenciasEstudos1 = new HashSet<PrecedenciasEstudos>();
        RegistosCAD = new HashSet<RegistosCAD>();
    }

    public int id { get; set; }
    public int idProjetos { get; set; }
    public int idProgramas { get; set; }

    [Required]
    [StringLength(25)]
    public string NomeEstudo { get; set; }

    [Required]
    [StringLength(5)]
    public string Utilizador { get; set; }

    public DateTime DataInicial { get; set; }

    public DateTime? DataFinal { get; set; }

    public bool Producao { get; set; }

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage","CA2227:CollectionPropertiesShouldBeReadOnly")]
    public virtual ICollection<EstadosEstudo> EstadosEstudo { get; set; }

    public virtual Programas Programas { get; set; }

    public virtual Projetos Projetos { get; set; }

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage","CA2227:CollectionPropertiesShouldBeReadOnly")]
    public virtual ICollection<HistoricoDetalhadoEstudo> HistoricoDetalhadoEstudo { get; set; }

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage","CA2227:CollectionPropertiesShouldBeReadOnly")]
    public virtual ICollection<PrecedenciasEstudos> PrecedenciasEstudos { get; set; }

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage","CA2227:CollectionPropertiesShouldBeReadOnly")]
    public virtual ICollection<PrecedenciasEstudos> PrecedenciasEstudos1 { get; set; }

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage","CA2227:CollectionPropertiesShouldBeReadOnly")]
    public virtual ICollection<RegistosCAD> RegistosCAD { get; set; }
}

还有类Projetos：

public partial class Projetos
{
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage","CA2214:DoNotCallOverridableMethodsInConstructors")]
    public Projetos()
    {
        Caracteristicas = new HashSet<Caracteristicas>();
        Estudos = new HashSet<Estudos>();
    }

    public int id { get; set; }

    [Required]
    [StringLength(15)]
    public string projeto { get; set; }

    public int id_Tipo { get; set; }

    [StringLength(50)]
    public string Cliente { get; set; }

    [StringLength(50)]
    public string Designacao { get; set; }

    public int? id_Pais { get; set; }

    public int? CalculoEletrico { get; set; }

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage","CA2227:CollectionPropertiesShouldBeReadOnly")]
    public virtual ICollection<Caracteristicas> Caracteristicas { get; set; }

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage","CA2227:CollectionPropertiesShouldBeReadOnly")]
    public virtual ICollection<Estudos> Estudos { get; set; }

    public virtual Paises Paises { get; set; }

    public virtual TiposProjeto TiposProjeto { get; set; }
}

我注意到的一件事是，当我在数据库中查询“ Estudo”时，没有得到导航属性“ Projetos”，但是当我向数据库询问“ Projeto”时，却得到了导航属性“ Estudos”。 “。

另一件事是，当我在数据库中查询“ Estudo”时，没有获得导航属性“ Projetos”，但是如果我在数据库中查询了“ Projeto”，其中id = Estudo.idProjetos，则导航“ Estudos”中以前为空的“ Projetos”属性会自动填充关联的“ Projeto”的值。

那么，有人有解决此问题的提示吗？

感谢您的帮助。

解决方法

您可以在Estudos实体中向ForeignKey和Programas属性添加Projetos属性。

[ForeignKey("idProgramas")]
public virtual Programas Programas { get; set; }

[ForeignKey("idProjetos")]
public virtual Projetos Projetos { get; set; }

在查询Estudos时，请包含Programas和Projetos。 

db.Estudos
  .Include(x => x.Programas)
  .Include(x => x.Projetos)
  .ToList();

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