使用LINQ实现搜索过滤器时出现问题

Question

I'm trying to implement a search filter using LINQ in my ASP.Net application.

However I'm running into problems. Here is my code:

var result = (from x in db.ContactSet
    select new Models.Contact
    {
        AccountId = x.AccountId,
        FirstName = x.FirstName,
        LastName = x.LastName,
        FullName = x.FullName,
        JobTitle = x.JobTitle,
        ParentCustomerId = x.ParentCustomerId,
        EMailAddress1 = x.EMailAddress1,
        Telephone1 = x.Telephone1,
        MobilePhone = x.MobilePhone,
        Fax = x.Fax,
        GenderCode = x.GenderCode,
        BirthDate = x.BirthDate
    }); //? Gets all rows

result = result
    .Where(x =>
        x.FirstName.Contains(model.searchPhrase) ||
        x.LastName.Contains(model.searchPhrase)); //? Search Filter

The Gets all rows code works perfectly in getting all the rows from my database. However I'm having issues with the Search Filter part of the code.

model.searchPhrase is a null-able string.

Every time I run through the Search Filter nothing gets returned (doesn't matter what the input is.

After debugging I noticed that after that block of code runs I get the following Exception Error :

Static members: 'NotSupportedException' is a type, which is not valid in the given context. Non-public members: 'new System.Linq.SystemCore_EnumerableDebugView(result).items' thew an exception of type 'System.NotSupportedException'

Any idea what's wrong here?

Answer 1

I've written a library to help with this problem and make it easier to build conditional queries for filtering. You can get the package from NuGet here: https://www.nuget.org/packages/LinqConditionalExtensions

Your code could be rewritten as:

var hasFilter = !string.IsNullOrWhiteSpace(model.searchPhrase);

var result = db.ContactSet
    .WhereIf(hasFilter, x => x.FirstName.Contains(model.searchPhrase) || x.LastName.Contains(model.searchPhrase))
    .Select(x => new Models.Contact
    {
        AccountId = x.AccountId,
        FirstName = x.FirstName,
        LastName = x.LastName,
        FullName = x.FullName,
        JobTitle = x.JobTitle,
        ParentCustomerId = x.ParentCustomerId,
        EMailAddress1 = x.EMailAddress1,
        Telephone1 = x.Telephone1,
        MobilePhone = x.MobilePhone,
        Fax = x.Fax,
        GenderCode = x.GenderCode,
        BirthDate = x.BirthDate
    });

The WhereIf() method will only apply the filter if the condition is true. In this case, if your model's search-phrase is not null or white-space.

You can read more about it here: https://github.com/xKloc/LinqConditionalExtensions

Answer 2

model.searchPhrase is a null-able string as he written. You cannot compare data type null-able variable with data type (string variable) in LINQ Query. So, it is throwing exception.

Use following code. It worked for me

string SearchValue="";
try
{SearchValue=model.searchPhrase.Tostring();}catch{}

result = result.Where(x => x.FirstName.Contains(SearchValue) ||
        x.LastName.Contains(SearchValue)).ToList();