Question

使用EF。

处理MVC 5应用程序

我的数据库中有3个表。举个简单的例子让我用这个....

汽车
- 编号
- CarName
颜色
- 编号
- ColorName
CarsColors
- CarId
- ColorId

汽车和颜色是“主”表。 CarsColors是一个包含各种组合的交叉引用表。

目标：创建一个显示表格的视图。对于每一行，它将显示汽车详细信息。将有一个“颜色”列。在“颜色”列中，将有一个逗号描述的汽车使用的颜色列表。（这是我问题的核心。）所以，例如....

NSTask *usbCommandTask;
NSPipe *outPipe;
NSPipe *inPipe;
NSPipe *errorPipe;
NSFileHandle *inFile;
NSFileHandle *outFile;
NSTimer *pollTimer;
dispatch_queue_t mtpTask;

@implementation AppDelegate


- (void)commandNotification:(NSNotification *)notification
{
    NSData *data = nil;

    while ((data = [outFile availableData]) && [data length]){
        NSString *myString = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
        NSLog(@"Data: %@",myString);
        }
    NSLog(@"Execution never gets here");

}

-(void)checkTask
{
    if(usbCommandTask){
        if([usbCommandTask isRunning])NSLog(@"Task running"); else NSLog(@"Task dead");

    } else NSLog(@"Task is nil");


}

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {



    usbCommandTask = [[NSTask alloc] init];
    [usbCommandTask setLaunchPath:@"/Applications/usb-debugger-cli"];
    [usbCommandTask setCurrentDirectoryPath:@"/"];
    [usbCommandTask setArguments:[NSArray arrayWithObject:@"-i"]];
    inPipe = [NSPipe pipe];
    [usbCommandTask setStandardInput:inPipe];




    outPipe = [NSPipe pipe];
    [usbCommandTask setStandardOutput:outPipe];
    errorPipe = [NSPipe pipe];
    [usbCommandTask setStandardError:errorPipe];

    outFile = [outPipe fileHandleForReading];
    inFile = [inPipe fileHandleForWriting];

     [outFile waitForDataInBackgroundAndNotify];



    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(commandNotification:)
                                                 name:NSFileHandleDataAvailableNotification
                                               object:nil];



    pollTimer=[NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:@selector(checkTask) userInfo:nil repeats:TRUE];
    [usbCommandTask launch];
    NSLog(@"Launched");



}


- (void)applicationWillTerminate:(NSNotification *)aNotification {
    // Insert code here to tear down your application
    if(usbCommandTask)[usbCommandTask terminate];


}


- (IBAction)clicked:(id)sender {

    if(usbCommandTask){
    NSString *command=@"help\n";
    NSData *commandData=[NSData dataWithBytes:command.UTF8String length:command.length];

    [inFile writeData:commandData];
    }
    else
    {NSLog(@"Comamnd task dead");
    }
}

我不确定如何做到这一点。我知道我的汽车选择我可以使用.Include（）来包含CarsColors。但是，我如何“升级”一个级别才能获得Cars.ColorName？我需要循环通过CarsColors以填充每行的最后一列，但使用Colors表作为实际颜色名称。

由于

Answer 1

您可以使用导航属性来获取颜色名称：

public partial class CarsColors
{
    public int CarId { get; set; }
    public int ColorId { get; set; }

    public virtual Car Car { get; set; }
    public virtual Color Color { get; set; }
}

因此，如果您拥有CarsColors类型的对象，则可以阅读Color名称，如下所示：

obj.Color.ColorName

像下面这样的东西可以满足您的需求：

var cars = dbContext.Cars
                    .Include(car=>car.CarsColors)
                    .GroupBy(car=>car.CarName)
                    .Select(gr=> new 
                    {
                        CarName = gr.Key,
                        Colors = string.Join(",", gr.Select(car=>car.CarsColors.Color.ColorName))
                    });

从二级表（实体框架）获取数据

1 个答案: