如何在一个控制器/JOIN 中从我的数据库返回/获取两个模型/表或使用存储过程

Question

I am trying to create get request that when provided with a broker ID, it returns all the broker information from the Broker table and all of the brokers Applications from the Application table. The two tables are joined by broker ID.

I have tried a few methods found on stakoverflow but keep hitting errors.

public class BrokerApplications
    {
        public virtual ICollection<Broker> Broker { get; set; }
        public virtual ICollection<Application> Applications { get; set; }
    }

    

I tried

[HttpGet("{id}")]
        public async Task<ActionResult<BrokerApplications>> GetBrokerApplicationsAsync(int brokerID)
        {
                var brokerApps = (from b in _context.Broker
                                  join a in _context.Application on b.BrokerId equals a.BrokerId
                                  where a.BrokerId == brokerID
                                  //            select new { b.BrokerForename, b.BrokerId, a.RollNumber, a.CustomerFullName }
                                  //).ToList();
                                  select a);
    
                return brokerApps;
}

But got an error message saying

"cs0029:cannot implicitly covert type 'System.Linq.IQueryable<SMWEBAPI.Models.Application> to 'Microsoft.AspNetCore.Mvc.ActionResult<SMWebAPI.Controllers.BrokerAppsController.BrokerApplicattions>

This is when I tried

[HttpGet("{id}")] public async Task<ActionResult> GetBrokerApplicationsAsync(int brokerID) { var broker = await _context.Broker.FindAsync(brokerID);

            BrokerApplications BrokerApps = new BrokerApplications();

            List<Application> lstApps = new List<Application>();
            lstApps = (List<Application>)_context.Application.Where(a => a.BrokerId == brokerID);
            BrokerApps.Broker = (ICollection<Broker>)broker.ToList();
            BrokerApps.Applications = lstApps;

            return BrokerApps;

}

but this return the following error message when I tried to call from the URL

InvalidCastException: Unable to cast object of type 'Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable 1[SMWebAPI.Models.Application]' to type 'System.Collections.Generic.List 1[SMWebAPI.Models.Application]'. SMWebAPI.Controllers.BrokerAppsController.GetBrokerApplications(int brokerID) in BrokerAppsController.cs + lstApps = (List)_context.Application.Where(a => a.BrokerId == brokerID);

Can someone please help me in how to return from this Get method when provided with a brokerID please?

---

UPDATE

I haven't been able to return the data as of yet, as when I used a method that didn't give me any errors it returned an empty array.

[HttpGet("{id}")]
    public async Task<ActionResult<BrokerApplications>> GetBrokerApplicationsAsync(int brokerID)
    {
        return new BrokerApplications()
        {
            Broker = await _context.Broker.Where(x => x.BrokerId == brokerID).ToListAsync(),
            Applications = await _context.Application.Where(a => a.BrokerId == brokerID).ToListAsync()
        };
    }

SO...

I wanted to find another way to get the data.

I have created a stored procedure

    -- =======================================================
-- Create Stored Procedure Template for Azure SQL Database
-- =======================================================
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
-- =============================================
-- Author:      <Author, , Name>
-- Create Date: <Create Date, , >
-- Description: <Description, , >
-- =============================================
CREATE PROCEDURE ApplicationsByBroker
(
    -- Add the parameters for the stored procedure here
    @brokerId int
)
AS
BEGIN
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON

    -- Insert statements for procedure here
    SELECT dbo.Application.*, dbo.Broker.*
  FROM dbo.Application, dbo.Broker
WHERE (dbo.Broker.BrokerID = @brokerId AND dbo.Application.BrokerID = 
    @brokerId)

    END
    GO

I ran this to ensure it worked using

USE SecuredMessagingDatabase;  
GO  
EXEC dbo.ApplicationsByBroker @BrokerId = 1000001;

And I got the expected results, How would I execute this in my web api?

Answer 1

It's better to use Include if two objects have a relation by BorkerId , but you can write like this to solve the problem:

[HttpGet("{id}")]
public async Task<ActionResult<BrokerApplications>> GetBrokerApplicationsAsync(int brokerID)
{
   return new BrokerApplications()
   {
    Broker = await _context.Broker.Where(x=>x.Id==brokerID).ToListAsync(),
    Applications = await _context.Application.Where(a => a.BrokerId == brokerID).ToListAsync()
   };

  
}

Answer 2

Try the following query, which have one roundtrip to database. I hope EF will not fail.

class BrokerApplication
{
   public Broker Broker {get; set;)
   public Application Application {get; set;)
}

[HttpGet("{id}")]
public async Task<ActionResult<BrokerApplications>> GetBrokerApplicationsAsync(int brokerID)
{
   var brokers = _context.Broker.Where(x => x.Id == brokerID)
      .Select(b => new BrokerApplication { Broker = b });

   var applications = _context.Application.Where(a => a.BrokerId == brokerID) 
      .Select(a => new BrokerApplication { Application = a });

   var combined = await brokers.Concat(applications).ToListAsync();

   var result = BrokerApplications
   {
     Broker = combined.Where(c => c.Broker != null)
       .Select(c => c.Broker).ToList(),
     Applications = combined.Where(c => c.Application != null)
       .Select(c => c.Application).ToList()
   };
 
   return result;
}