实体框架6将自定义SQL查询映射到实体

Question

I am very new to ASP.NET MVC and Entity Framework at the moment. I've been working with it for about 3 months at the current moment in time.

I have an ASP.NET MVC 5 application that's running Entity Framework 6. This is a code first approach from an existing database with auto migrations enabled so all of my Entity classes are auto generated. I am trying to add a view to my MVC application that returns a specific result set. Currently the previous developer has the application set up to only accept an Entity class to display data to a DataTable DataTables.net . To clarify further:

I have two Entity tables in my model that are tables in MySQL.

| Samples           | SampleLocation |
|:------------------|---------------:|
| Id                |     LocationId |        
| DateAssigned      |           Name |      
| CheckedInDate     |           Size |         
| SampleLocationId  |                |        
| ...etc            |         ...etc |          

What I'm trying to accomplish is querying both tables and returning the results to my MVC application in a view. From there run an Update and update a couple of columns in the Samples table. Below is the roughly the query that returns the results I need.

SELECT Samples.Id, samples.CheckedInDate, SampleLocation.Name, SampleLocation.Size, 
SampleLocation.LocationId 
FROM (Samples join SampleLocation 
ON ((Samples.SampleLocationId = SampleLocation.LocationId))) 
WHERE  isnull(samples.CheckedInDate) ORDER BY samples.Id

From the research that I have done there are a few ways to accomplish this. The ways that I've tried that would give me a class I could use are creating a stored procedure and then updating the model - this breaks the model and unmaps every single entity in the model. I have tried creating a view with the query to add to the model - but this breaks it as well and unmaps everything. I later found out that this is a bug.

So my question is, how can I map a query to an Entity that return results to a view? Is there a better way to go about this?

Answer 1

There are several ways to accomplish what you want to do, using either Entity Framework only or extra tools like Dapper

Entity Framework Only:

First you can use Linq to extract the data, I'll look something like this:

var list = from s in Samples
           join l in SampleLocations
               on s.Id equals l.LocationId
           where s.CheckedInDate == null
           select new
           {
                s.Id,
                s.CheckedInDate,
                l.Name,
                l.Size, 
                l.LocationId 
           };

Dapper:

The second method is using dapper, the only real difference here is that you would be working with your queries directly, so instead of linq you had something like this:

Connection.Query(@"SELECT Samples.Id, samples.CheckedInDate,  
                     SampleLocation.Name, SampleLocation.Size, 
                     SampleLocation.LocationId 
                   FROM Samples
                     join SampleLocation 
                       ON Samples.SampleLocationId = SampleLocation.LocationId
                   WHERE isnull(samples.CheckedInDate) ORDER BY samples.Id");

For both:

In your update method, you first have to retrieve the entities, for that you can use the DbSet.Find method or another query, after that you call DbConext.SaveChanges .

Answer 2

This is the solution to my problem. Basically manually creating an Entity within the XML and mapping it to a virtual table. Entity Framework DefiningQuery