为什么此Linq Where子句不过滤结果

Question

I am new to Linq and MVC and it has taken a lot of searching and learning to get to this point.

I have the following method that successfully receives the parameter "code".

    public ActionResult GetIssueList(string code)
    {
        //dynamic fill of project code dropdown on selection of customer code drop down
        ProjectManager pm = new ProjectManager();

        var projectcodes = pm.SelectAllProjects();
        var projects = new List<Project>();

        foreach (var proj in projectcodes)
        {
            projects.Add(proj as Project);
        }
        return Json(projects.Where(x => x.CustomerCode == code).ToList());
    }

The data is being retrieved from the database but the where clause does not filter out data that is equal to the parameter.

Answer 1

Debug through execution and make sure that the items certainly do not have the CustomerCode of code . My question for you though is "are the items in projectcodes Project objects? if they are not, you cannot as cast them to Project , but instead must make new Projects with that code new Project(projectCode)

Also, everything you had written above could easily be re-written as one line of code. (you may have to do a .ToList<Project>() before the Where , but I don't know your types so I won't assume)

public ActionResult GetIssueList(string code)
{
    return Json(new ProjectManager()
        .SelectAllProjects()
        .Select(proj => proj as Project)
        .Where(proj => proj.CustomerCode == code)
        .ToList();
}

Edit : Place a breakpoint in your above method on the return statement, and check before the comparison happens if the items in the list have the expected CustomerCode.

Answer 2

There are too many unknowns here to answer more precisely, but to more easily debug step-by-step, I suggest you change the Where call to a traditional loop (and change it back once you found the problem, of course):

public ActionResult GetIssueList(string code)
{
    IEnumerable<Project> projects =
        new ProjectManager()
        .SelectAllProjects()
        .Cast<Project>();

    //this is replacement for Where call.
    //Debug breakpoint here step by step and look at the CustomerCode values
    //to find out why they are all added.
    List<Project> filtered = new List<Project>();
    foreach(Project p in projects)
    {
        if(p.CustomerCode == code)
            filtered.Add(p);
    }

    return Json(filtered);
}