如何将数据从Sql对象复制到C#模型属性

我有两张桌子

>员工：Id,Name,DepartmentId
>部门：Id,Name

Employee.cs：

public int Id {get;set;}
public string Name {get;set;}
public int DepartmentId {get;set;}

Department.cs：

public int Id {get;set;}
public string Name {get;set;}

ViewModel：EmployeeDepartmentVM：

public Department department {get;set;}
public List<Employee> employees {get;set;}

要加入这两个表,我写了这个代码：

SELECT E.*,D.Id as DId,D.Name as DName 
     from [Employee] as E
     LEFT OUTER JOIN [Department] as D
     ON E.DepartmentId = D.Id
     where D.Id = 1

如何从上述查询获取EmployeeDepartmentVM类型？

我知道如果我写一个像我的问题的模型将会解决：

public int Id {get;set;}
public string Name {get;set;}
public int DepartmentId {get;set;}
public int DId {get;set;}
public string Name {get;set;}

但我不想写额外的模型.只需要将查询数据绑定到EmployeeDepartmentVM类型中.

解决方法

这导致如下：

static List<EmployeeDepartmentVM> GetEmployeeDepartmentVMList(DbCommand command)
{
    var resultById = new Dictionary<int,EmployeeDepartmentVM>();
    using (var reader = command.ExecuteReader())
    {
        var employeeIdCol = reader.GetOrdinal("Id");
        var employeeNameCol = reader.GetOrdinal("Name");
        var departmentIdCol = reader.GetOrdinal("DId");
        var departmentNameCol = reader.GetOrdinal("DName");
        while (reader.Read())
        {
            var departmentId = reader.GetInt32(departmentIdCol);
            EmployeeDepartmentVM result;
            if (!resultById.TryGetValue(departmentId,out result))
            {
                result = new EmployeeDepartmentVM
                {
                    department = new Department(),employees = new List<Employee>()
                };
                result.department.Id = departmentId;
                result.department.Name = reader.GetString(departmentNameCol);
                resultById.Add(departmentId,result);
            }
            var employee = new Employee();
            employee.Id = reader.GetInt32(employeeIdCol);
            employee.Name = reader.GetString(employeeNameCol);
            employee.DepartmentId = departmentId;
            result.employees.Add(employee);
        }
    }
    return resultById.Values.ToList();
}

有些事情要注意写入的方式,您的SQL查询意味着Department相关的字段可以为null(LEFT OUTER JOIN).但是,WHERE子句和Employee模型(DepartmentId字段不可为空)意味着它不会发生.如果意图包括没有员工的部门,则更好地将联接更改为RIGHT OUTER,并使用以下内容：

// ...
if (reader.IsDBNull(employeeIdCol)) continue;
var employee = new Employee();
// ...

编辑：为了完整,这里是另一种方法.它类似于EF实现类似查询的方式,不需要临时字典,但要求输入集由主表的PK排序,因此您需要添加

ORDER BY D.Id

在你的SQL的结尾.数据库可以轻松有效地提供这样的排序,并且此解决方案的优点在于它允许延迟执行,并且不需要处理整个集合以便开始返回结果.如果您想要获得列表并不重要,但在其他情况下可能会有用.

static IEnumerable<EmployeeDepartmentVM> GetEmployeeDepartmentVMs(DbCommand command)
{
    using (var reader = command.ExecuteReader())
    {
        var employeeIdCol = reader.GetOrdinal("Id");
        var employeeNameCol = reader.GetOrdinal("Name");
        var departmentIdCol = reader.GetOrdinal("DId");
        var departmentNameCol = reader.GetOrdinal("DName");
        for (bool more = reader.Read(); more;)
        {
            var result = new EmployeeDepartmentVM
            {
                department = new Department(),employees = new List<Employee>()
            };
            result.department.Id = reader.GetInt32(departmentIdCol);
            result.department.Name = reader.GetString(departmentNameCol);
            do
            {
                if (reader.IsDBNull(employeeIdCol)) continue;
                var employee = new Employee();
                employee.Id = reader.GetInt32(employeeIdCol);
                employee.Name = reader.GetString(employeeNameCol);
                employee.DepartmentId = result.department.Id;
                result.employees.Add(employee);
            }
            while ((more = reader.Read()) && reader.GetInt32(departmentIdCol) == result.department.Id);
            Debug.Assert(!more || reader.GetInt32(departmentIdCol) > result.department.Id); // Sanity check
            yield return result;
        }
    }
}

要按照第一种方法获得列表,只需在调用后添加ToList()即可.

var result = GetEmployeeDepartmentVMs(command).ToList();

（编辑：安卓应用网）

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