c# - 如何使用 LINQ MVC 基于 AND 条件应用搜索过滤

Question

我正在做 asp.net-mvc 项目

我想使用带(AND 条件)的 LINQ 根据参数(大多数是 Veiw 中的下拉列表)过滤记录，但我的问题是 null 或空参数。

有时，用户根据一个或两个字段过滤记录，而其余字段值返回为空。则没有满足条件的结果。

目前我使用(或条件)来获取想要的记录:

 public ActionResult Search(int? ReportID, int? ReportName, int? Department, string ManagerConfirmationState1, string RiskLevel, string NoteType)
    {




        ViewBag.ReportID = new SelectList(db.Reports, "ReportID", "ReportID");
        ViewBag.ReportName = new SelectList(db.Reports, "ReportID", "ReportName");
        ViewBag.Department = new SelectList(db.Departments, "DepartmentID", "DepartmentName");
        ViewBag.ManagerConfirmationState1 = new SelectList(db.ManagerConfirmationState1, "ManagerConfirmationState1ID", "ManagerConfirmationState11");
        ViewBag.RiskLevel = new SelectList(db.RiskLevels, "RiskLevelID", "RiskLevel1");
        ViewBag.NoteType = new SelectList(db.NoteTypes, "NoteTypeID", "NoteType1");

        var Notes = from n in db.Notes
                    select n;


        //filteration

        Notes = Notes.Where(n => n.ReportID == ReportID
                                   || n.Report.ReportID == ReportName
                                   || n.Report.Department.DepartmentID == Department
                                   || n.ManagerConfirmationState1.Equals(ManagerConfirmationState1)
                                   || n.RiskLevel.Equals(RiskLevel)
                                   || n.NoteType.Equals(NoteType));




        return View(Notes.ToList());
    }

一 block View :

@using (@Html.BeginForm("Search", "Notes", null, FormMethod.Post))
{

    <div class="form-horizontal">

        <div class="col-md-6">

            <div class="form-group">

                <label class="control-label col-md-2">رقم التقرير</label>
                <div class="col-md-10">
                    @Html.DropDownList("ReportID", null, "اختـر", htmlAttributes: new { @class = "form-control" })

                </div>
            </div>

            <div class="form-group">

                <label class="control-label col-md-2">التقرير</label>
                <div class="col-md-10">
                    @Html.DropDownList("ReportName", null, "اختـر", htmlAttributes: new { @class = "form-control" })

                </div>
            </div>


            <div class="form-group">

                <label class="control-label col-md-2">نوع الملاحظة</label>
                <div class="col-md-10">
                    @Html.DropDownList("NoteType", null, "اختـر", htmlAttributes: new { @class = "form-control" })

                </div>
            </div>

        </div>


        <div class="col-md-6">

            <div class="form-group">

                <label class="control-label col-md-2">الإدارة</label>
                <div class="col-md-10">
                    @Html.DropDownList("Department", null, "اختـر", htmlAttributes: new { @class = "form-control" })

                </div>
            </div>

            <div class="form-group">

                <label class="control-label col-md-2">اعتماد المدير</label>
                <div class="col-md-10">
                    @Html.DropDownList("ManagerConfirmationState1", null, "اختـر", htmlAttributes: new { @class = "form-control" })

                </div>
            </div>

            <div class="form-group">

                <label class="control-label col-md-2">درجة المخاطرة</label>
                <div class="col-md-10">
                    @Html.DropDownList("RiskLevel", null, "اختـر", htmlAttributes: new { @class = "form-control" })

                </div>
            </div>



        </div>





        <div class="form-group">
            <div class="col-md-offset-2 col-md-10">
                <input type="submit" value="بحث" class="btn btn-default" />
            </div>
        </div>


    </div>


}

总结:

我可以在 LINQ 中应用忽略空输入的过滤吗？

有什么建议吗？

Answer 1

只需逐步构建查询:

if (field1.HasValue) {
  query = query.Where(x => x.Val1 = field1.Value);
}
if (field2.HasValue) {
  query = query.Where(x => x.Val2 = field2.Value);
}

(因为 x.Where(y => cond1(y) && cond2(y)) 在功能上等同于 x.Where(y => cond1(y)).Where (y => cond2(y)).