如何将linq中的值解析为实体？

Question

I want to do something like this:

var apps = from app in context.Apps
    where (platform == AppPlatform.All ||
    (app.Platform == sPlatform && new Version(app.PlatformVersion) <= version))&&
    (availability == AppAvailability.All || app.Availability == sAvailability)
    select app;
return apps.ToList();

The line new Version(app.PlatformVersion) <= version)) is causing an error: Only parameterless constructors and initializers are supported in LINQ to Entities.

Basically what I need is to make my entity model parse the app.PlatformVersion as a new Version() object, instead of string, but I apparently can't do this from within my linq-to-entity. Can I do this at the entity-model level? I have other fields (strings) that I'd like to parse into types as well (like parsing a string to an Enum). How would I accomplish this?

Answer 1

Because EF tries to translate the Linq query to SQL and there is no way to translate Version method. So you could just query with other conditions first and store it in memory, then query from the in-memory object using the complex Linq query.

Technically you could do this, (you can definitely make it better in terms of the performance)

var apps_temp = from app in context.Apps.All().ToList();

//this query will not be translated to SQL.
var apps = from app in apps_temp
    where (platform == AppPlatform.All ||
    (app.Platform == sPlatform && new Version(app.PlatformVersion) <= version))&&
    (availability == AppAvailability.All || app.Availability == sAvailability)
    select app;


return apps.ToList();