如何从 IQueryable 获取计数

Question

我正在我的 GridView 中实现分页。来自this的文章，我需要两个方法：

public IQueryable BindEmployees(int startRowIndex, int maximumRows)
{
    EmployeeInfoDataContext dbEmp = new EmployeeInfoDataContext();
    var query = from emp in dbEmp.Employees
                join dept in dbEmp.Departments
                    on emp.DeptID equals dept.DeptID
                select new
                {
                    EmpID = emp.EmpID,
                    EmpName = emp.EmpName,
                    Age = emp.Age,
                    Address = emp.Address,
                    DeptName = dept.DepartmentName
                };

    return query.Skip(startRowIndex).Take(maximumRows);
} 

和

public int GetEmployeeCount()
{
    // How can I not repeat the logic above to get the count?
}

如何从第一种方法BindEmployees 中获取第二种方法GetEmployeeCount 的值？我的意思是不重复逻辑（查询）？

Answer 1

@Marc Gravell 的回答解决了上述问题，并且可能是最好的方法。但是，为了提供选项，您也可以重复join（因为您在计数时不需要匿名类型）：

private int GetEmployeeCount(EmployeeInfoDataContext dbEmp)
{
    var query = from emp in dbEmp.Employees
                join dept in dbEmp.Departments on emp.DeptID equals dept.DeptID
                select dept;

    return query.Count();
}

Answer 2

创建一个在两个地方都使用的函数：

//Can be private or public, your choice
private IQueryable<Employee> GetQuery()
{
    EmployeeInfoDataContext dbEmp = new EmployeeInfoDataContext();
    return from emp in dbEmp.Employees
                join dept in dbEmp.Departments
                    on emp.DeptID equals dept.DeptID
                select emp;
}

然后在你的其他两个函数中使用它：

public int GetEmployeeCount()
{
    return GetQuery().Count();
}

public IQueryable BindEmployees(int startRowIndex, int maximumRows)
{
    var query = from e in GetQuery()
                select new { /*Do your anonymous type here*/ };
    return query.Skip(startRowIndex).Take(maximumRows);
} 

Answer 3

一种选择是：

public IQueryable BindEmployees(int startRowIndex, int maximumRows, out int count)
{
    EmployeeInfoDataContext dbEmp = new EmployeeInfoDataContext();
    var query = from emp in dbEmp.Employees
                join dept in dbEmp.Departments
                    on emp.DeptID equals dept.DeptID
                select new
                {
                    EmpID = emp.EmpID,
                    EmpName = emp.EmpName,
                    Age = emp.Age,
                    Address = emp.Address,
                    DeptName = dept.DepartmentName
                };

    count = query.Count();
    return query.Skip(startRowIndex).Take(maximumRows);
}

另一种选择是将查询传递给分页函数。