.netcorelinqselect多載索引不起作用

在添加 Select 索引多載之前，我得到了一個 linq lambda 選擇代碼。之前，我得到了記錄串列，但我需要用于為每條記錄分配唯一 ID 的索引。當我添加 with 時ToList()，我得到一個沒有錯誤/內部例外的例外。我可以讓代碼不引發錯誤的唯一方法是使用.AsEnumberable()，但我需要一個串列。我閱讀了許多.ToList()適用于超載的帖子，但我沒有成功。

這是我的代碼和我試圖解決這個問題

  var emps = this.DbContext.Employees
                    .GroupJoin(this.DbContext.Depts,
                        employee => employee.EmployeeId,
                        dept => dept.EmployeeId,
                        (employee, dept) => new { employee, dept }
                    )
                    .SelectMany(
                        employee_dept_left => employee_dept_left.dept.DefaultIfEmpty(),
                        (employee_dept_left, dept) => new { employee_dept_left, dept }
                    )
                    .Join(this.DbContext.Divs,
                        emp_emp_dept => emp_emp_dept.employee_dept_left.employee.DivId,
                        division => division.DivId,
                        (emp_emp_dept, division) => new { emp_emp_dept, division }
                    )
                    .Where(s => !string.IsNullOrEmpty(filter.selectedDiv))
                    .GroupBy(grouped => new
                    {
                        grouped.emp_emp_dept.employee_dept_left.employee.EmployeeId,
                        grouped.emp_emp_dept.employee_dept_left.employee.LastNm,
                        grouped.emp_emp_dept.employee_dept_left.employee.FirstNm,
                        grouped.emp_emp_dept.employee_dept_left.employee.DivId
                    })
                    .Select((joined, index) => new EmployeeViewModel
                    {
                        Id = index,
                        EmployeeId = joined.Key.EmployeeId,
                        LastNm = joined.Key.LastNm.Trim(),
                        FirstNm = joined.Key.FirstNm.Trim(),
                        DivisionId = joined.Key.DivId,
                    }).ToList();

錯誤訊息說

無法翻譯。以可翻譯的形式重寫查詢，或通過插入對“AsEnumerable”、“AsAsyncEnumerable”、“ToList”或“ToListAsync”的呼叫顯式切換到客戶端評估。有關詳細資訊，請參閱https://go.microsoft.com/fwlink/?linkid=2101038。

我嘗試使用.AsEnumerable()而不是.ToList()：

List<EmployeeViewModel> test = emps.Cast<EmployeeViewModel>().ToList();

但這會引發例外。

任何幫助是極大的贊賞。

提前致謝

uj5u.com熱心網友回復：

問題Select是目前無法轉換為 SQL。您可以進行額外的選擇來解決問題AsEnumerable()。

    ...
    .Select(joined => new 
    {
        EmployeeId = joined.Key.EmployeeId,
        LastNm = joined.Key.LastNm.Trim(),
        FirstNm = joined.Key.FirstNm.Trim(),
        DivisionId = joined.Key.DivisionId,
    })
    .AsEnumerable()
    .Select((x, index) => new EmployeeViewModel
    {
        Id = index,
        EmployeeId = x.EmployeeId,
        LastNm = x.LastNm,
        FirstNm = x.FirstNm,
        DivisionId = x.DivisionId,
    }).ToList();

請注意，當存在連接時，查詢語法在查詢語法中更具可讀性。

var query = 
    from employee in this.DbTracsContext.Employees
    join dept in his.DbTracsContext.Depts on employee.EmployeeId equals dept.EmployeeId into employee_dept_left
    from dept in employee_dept_left.DefaultIfEmpty()
    join division in this.DbTracsContext.Depts on employee.DivisionId equals division.DivisionId
    where string.IsNullOrEmpty(filter.DivisionSelection) || filter.DivisionSelection == "0" || employee.DivisionId == filter.DivisionSelection
    group employee by new { employee.EmployeeId, employee.LastNm, employee.FirstNm, employee.DivisionId } into g
    select new
    {
        EmployeeId = g.Key.EmployeeId,
        LastNm = g.Key.LastNm.Trim(),
        FirstNm = g.Key.FirstNm.Trim(),
        DivisionId = g.Key.DivisionId,
    };

var emps = query
    .AsEnumerable()
    .Select((x, index) => new EmployeeViewModel
    {
        Id = index,
        EmployeeId = x.EmployeeId,
        LastNm = x.LastNm,
        FirstNm = x.FirstNm,
        DivisionId = x.DivisionId,
    }).ToList();

標籤：林克 .net-core

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