Question

当覆盖ModelAdmin.save_model()时，我希望能够在对象的新值与旧值之间运行一些计算。有什么方法可以在更改之前获得包含所有先前数据的“旧对象”吗？

例如，如果我有Object obj.name =“foo”，我通过Django管理应用更新为obj.name =“bar”，保存以下内容后代码应该打印出来：

from django.contrib import admin

class ObjectAdmin(admin.ModelAdmin):
     def save_model(self, request, obj, form, change):
          old_object = self.get_old_object()
          print(old_object.name)  # Should print out "foo"
          print(obj.name)         # Should print out "bar"

Answer 1

所以你可以通过这样的数据库查找来获取对象

public class cameraf extends AppCompatActivity{
private Preview mPreview;
private Camera mCamera;
private static final String TAG = "Myact";
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_cameraf);
    mCamera = getCameraInstance();
    mPreview = new Preview(this, mCamera);
    FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
   preview.setOnTouchListener(new View.OnTouchListener(){
        public boolean onTouch(View v, MotionEvent event){
            Log.v(TAG, "will now take picture");
            mCamera.takePicture(null, null, mPicture);
            return true;
        }
    });
    preview.addView(mPreview);
}
private Camera.PictureCallback mPicture = new Camera.PictureCallback() {
    @Override
    public void onPictureTaken(byte[] data, Camera camera) {
        Log.v(TAG, "Getting output media file");
        File pictureFile = getOutputMediaFile(MEDIA_TYPE_IMAGE);
        if (pictureFile == null) {
            Log.v(TAG, "Error creating output file");
            return;}
        try {
            FileOutputStream fos = new FileOutputStream(pictureFile);
            fos.write(data);
            fos.close();
        } catch (FileNotFoundException e) {
            Log.v(TAG, e.getMessage());
        } catch (IOException e) {
            Log.v(TAG, e.getMessage());}
    }
};
public static final int MEDIA_TYPE_IMAGE = 1;
private static File getOutputMediaFile(int type){
        File mediaStorageDir = new File(Environment.getExternalStoragePublicDirectory(
            Environment.DIRECTORY_PICTURES), "MyCameraApp");
    if (! mediaStorageDir.exists()){
        if (! mediaStorageDir.mkdirs()){
            Log.d("MyCameraApp", "failed to create directory");
            return null;}
    }
    String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date());
    File mediaFile;
    if (type == MEDIA_TYPE_IMAGE){
        mediaFile = new File(mediaStorageDir.getPath() + File.separator +
                "IMG_"+ timeStamp + ".jpg");
    } else {
        return null;}
    return mediaFile;
}
public static Camera getCameraInstance(){
    Camera c = null;
    try {
        c = Camera.open(); // attempt to get a Camera instance
    }
    catch (Exception e){
    }
    return c; // returns null if camera is unavailable
}
public class Preview extends SurfaceView implements SurfaceHolder.Callback {
    private SurfaceHolder mHolder;
    private Camera mCamera;
    public Preview(Context context, Camera camera) {
        super(context);
        mCamera = camera;
        mHolder = getHolder();
        mHolder.addCallback(this);
        mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
    }
    public void surfaceCreated(SurfaceHolder holder) {
        try {
            mCamera.setPreviewDisplay(holder);
            mCamera.setDisplayOrientation(90);
            Camera.Parameters params = mCamera.getParameters();
            params.setFocusMode(Camera.Parameters.FOCUS_MODE_CONTINUOUS_PICTURE);
            params.setFlashMode(Camera.Parameters.FLASH_MODE_TORCH);
            mCamera.setParameters(params);
        } catch (IOException exception) {
            mCamera.release();
            mCamera = null;}
    }
    public void surfaceDestroyed(SurfaceHolder holder) {
        mCamera.stopPreview();
        mCamera.release();
        mCamera = null;
    }
    public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
        Camera.Parameters parameters = mCamera.getParameters();
        parameters.setPreviewSize(w, h);
        mCamera.startPreview();
    }
}
private void releaseCamera(){
    if (mCamera != null){
        mCamera.release();        // release the camera for other applications
        mCamera = null;
    }
}
}

如果您需要处理它不存在的情况，您可以

old_object = self.model.objects.get(id=obj.id)

此外，try: old_object = self.model.objects.get(id=obj.id) except self.model.DoesNotExist: ...只是设置为ModelAdmin中的模型类，因此您可以将其替换为模型类

在ModelAdmin中，如何在覆盖`save_model（）`时获取对象的先前值

1 个答案: