使用实体框架通过 ID 从其他表中获取值

Question

我有两个已经存在的表（没有外键）：

客户 (Id, Name, .....) 项目 (Id, CustomerId, name)

在我的 asp.net 核心应用程序中，我有两个模型：

public class Customer {
   public int Id { get; set; };
   public String Name { get; set; };
}

public class Project {
   public int Id { get; set; };
   public Customer Customer{ get; set; };
   public String Name{ get; set; };
}

以及用于此的数据上下文类

public class CustomerContext: DbContext
{
    public CustomerContext(DbContextOptions<CustomerContext> options) : base(options)
    {
    }

    public DbSet<CustomerContext> Customer { get; set; }
}

public class ProjectContext: DbContext
{
    public ProjectContext(DbContextOptions<ProjectContext> options) : base(options)
    {
    }

    public DbSet<ProjectContext> Project{ get; set; }
}

但我无法找到如何通过 customerId 获取 Projectclass 中的 Customer 对象

有人能帮助我吗？谢谢

编辑：现在我像下面的答案一样更改我的模型类

但是在加载页面时出现 SQL 异常 SqlException: Invalid object name 'Customer'。

        projectList = await (from project in _context.Project
                                     join customer in _customerContext.Customer on project.CustomerId equals customer.Id into tmp
                                     from m in tmp.DefaultIfEmpty()

                                     select new Project
                                     {
                                         Id = sollIst.Id,
                                         CustomerId = sollIst.CustomerId,
                                         Customer = m,
                                         Name = sollIst.Name,
                                     }
                      ).ToListAsync();

Answer 1

更新您的模型类，如下所示：

public class Customer {
   public int Id { get; set; };
   public String Name { get; set; };
}

public class Project {
   public int Id { get; set; };
   public String Name{ get; set; };
   public int CustomerID { get; set; }
   [ForeignKey("CustomerID")]
   public Customer Customer{ get; set; };
}

将两个 DbContext 合并为一个。

public class ProjectContext: DbContext
{
    public ProjectContext(DbContextOptions<ProjectContext> options) : base(options)
    {
    }

    public DbSet<Project> Projects { get; set; }
    public DbSet<Customer> Customers { get; set; }
}

然后执行

projectList = await (from project in _context.Project
                 join customer in _context.Customer on project.CustomerId equals customer.Id into tmp
                 from m in tmp.DefaultIfEmpty()

                 select new Project
                 {
                     Id = sollIst.Id,
                     CustomerId = sollIst.CustomerId,
                     Customer = m,
                     Name = sollIst.Name,
                 }
  ).ToListAsync();

我希望以下链接能帮助您了解如何跨不同数据库连接两个表。

1. 使用实体框架连接来自两个数据库的表。
2. 跨两个数据库的实体框架联接