DbComparisonExpression需要具有可比类型的参数

Question

我是新手使用Linq并尝试创建一个搜索按图表编号搜索并在新的操作视图中显示结果.运行代码时,我得到错误"DbComparisonExpression需要具有可比类型的参数".我相信这与搜索类型有关,字符串和图表编号是int,但我不知道如何解决问题.任何帮助将不胜感激!

控制器:

public ActionResult Index(string searchTerm = null)
{
    var model =
        db.Patient
        .Where(r => searchTerm == null || r.ChartNumber.Equals(searchTerm))
                .Select(r => new NewListModel
                {
                    ChartNumber = r.ChartNumber,
                    FirstName = r.FirstName,
                    LastName = r.LastName,
                }
                );
    return View(model);
}

模型:

public class NewListModel
{
    public int ChartNumber { get; set; }

    public string FirstName { get; set; }
    public string LastName { get; set; }

}

视图:

@model IEnumerable<Project.Models.NewListModel>
@{
    ViewBag.Title = "Home Page";
}

<form method="get">
    <input type="search" name="searchTerm" />
    <input type="submit" value="Search by Chart Number" />
</form>

@foreach (var item in Model)
{
    <div>
        <h4>@item.ChartNumber</h4>

    </div>
    <div>@item.FirstName</div>
    <div>@item.LastName</div>

}

新控制器

public ActionResult Index(string searchTerm = null)
        {
            int chartNo;
            if (searchTerm == null || Int32.TryParse(searchTerm, out chartNo)) {
            var model = db.Patient
            .Where(r => searchTerm == null || r.ChartNumber == chartNo)
            .Select(r => new NewListModel
                {
                    ChartNumber = r.ChartNumber,
                    FirstName = r.FirstName,
                    LastName = r.LastName,
                }
                );
             return View(model);
            } else {
                //Invalid number entered 
            }
            }

Answer 1

将数字条目转换为int：

int chartNo = 0;
if (searchTerm == null || Int32.TryParse(searchTerm, out chartNo)) {
    var model = db.Patient
        .Where(r => searchTerm == null || r.ChartNumber == chartNo)
        .Select(...);
    return ...;
} else {
    // Invalid number entered
}

或者使用 C# 7.0 输出变量功能：

if (searchTerm == null || Int32.TryParse(searchTerm, out int chartNo)) {
    var model = db.Patient
        .Where(r => searchTerm == null || r.ChartNumber == chartNo)
        .Select(...);
    return ...;
} else {
    // Invalid number entered
}