如何使用LINQ MVC基于AND条件应用搜索过滤

Question

我正在研究asp.net-mvc项目

我想基于参数过滤记录(大多数是Veiw中的下拉列表)使用LINQ with(AND condition),但我的问题是null或空参数.

有时用户过滤基于一个或两个字段的记录,其余字段值返回为空.那么没有结果符合条件.

目前我使用(OR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());
    }

一块视图:

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

                </div>
            </div>

            <div class="form-group">

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

                </div>
            </div>


            <div class="form-group">

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

                </div>
            </div>

        </div>


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

            <div class="form-group">

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

                </div>
            </div>

            <div class="form-group">

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

                </div>
            </div>

            <div class="form-group">

                <label class="control-label col-md-2">???? ????????</label>
                <div class="col-md-10">
                    @Html.DropDownList("RiskLevel", null, "?????", 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="???" class="btn btn-default" />
            </div>
        </div>


    </div>


}

摘要:

我可以在LINQ中使用忽略空输入来应用过滤吗？

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))在功能上相当于x.Where(y => cond1(y)).Where(y => cond2(y)).