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I have an object called Garage and once I first declare him, it has 4 parameters: garageName,garageId, garageCoordinatorPhone,garageProducts. I upload it to firebase. After some time I update the garage parameter in firebase: garageStocks. When I try getting the data out back to Garage class, I get the exeption:

com.google.firebase.database.DatabaseException: Expected a List while deserializing, but got a class java.util.HashMap

I looked at an almost exact question like this at: Expected a List while deserializing, but got a class java.util.HashMap

But it's answers doesn't make sense to me... I have been able to get the values even with lists of objects(see garageProducts).

GaragesActivity:

public class GaragesActivity extends AppCompatActivity {

    ArrayList<String> garages = new ArrayList<>();
    DatabaseReference dbReference = FirebaseDatabase.getInstance().getReference();
    RecyclerView rvGarages;
    Button tvGarageEdit;
    TextView tvGarageCoordinator;
    User selectedGarageCoordinator = null;
    boolean isEditable;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_garages);

        
        //defines the widgets
        rvGarages = findViewById(R.id.rvGarages);
        tvGarageEdit = findViewById(R.id.tvGarageEdit);

        refreshAllGarages();

        //defines and sets the toolbar in place.
        Toolbar toolbar = findViewById(R.id.app_bar);
        setSupportActionBar(toolbar);

        //defines the back button at the top corner
        ActionBar ab = getSupportActionBar();
        if(ab != null)
            ab.setDisplayHomeAsUpEnabled(true);


        tvGarageEdit.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //the opposite every press
                if (isEditable){
                    isEditable = false;
                    tvGarageEdit.setBackgroundColor(getResources().getColor(R.color.colorWritingImportant));
                }else{
                    isEditable = true;
                    tvGarageEdit.setBackgroundColor(getResources().getColor(R.color.colorLimeGreen));
                }
            }
        });
    }
    
    private void refreshAllGarages() {
        //reset
        garages.clear();
        GaragesAdapter myAdapter = new GaragesAdapter(GaragesActivity.this, garages);
        rvGarages.setAdapter(myAdapter);

        final Dialog myDialog = new Dialog(GaragesActivity.this);
        myDialog.setContentView(R.layout.dialog_progress);
        if(myDialog.getWindow() != null)
            myDialog.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));

        TextView tvAction = myDialog.findViewById(R.id.tvAction);
        tvAction.setText("טוען...");
        myDialog.show();

        // Read from the database
        Query q = dbReference.child("מחסנים").orderByKey();
        q.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                for (DataSnapshot AllGarages : dataSnapshot.getChildren()) //gets the list of Garages
                {
                    Garage g = AllGarages.getValue(Garage.class);
                    if(g.getGarageName() != null)
                        garages.add(g.getGarageName());
                }
                GaragesAdapter myAdapter = new GaragesAdapter(GaragesActivity.this, garages);
                rvGarages.setLayoutManager(new GridLayoutManager(GaragesActivity.this,4));
                myDialog.dismiss();
                rvGarages.setAdapter(myAdapter);
            }
            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
                throw databaseError.toException(); //Don't ignore errors
            }
        });

    }
}

Garage class:

public class Garage {

    private String garageName;
    private String garageId;
    private String garageCoordinatorPhone;
    private ArrayList<Product> garageProducts;
    private ArrayList<Product> borrowedProducts;
    private ArrayList<Product> damagedProducts;
    private ArrayList<Product> missingProducts;
    private ArrayList<Stock> garageStocks;

    public Garage(){}

    public Garage(String garageName, String garageCoordinatorPhone, String garageId, ArrayList<Product> garageProducts){
        this.garageProducts = garageProducts;
        this.garageName = garageName;
        this.garageCoordinatorPhone = garageCoordinatorPhone;
        this.garageId = garageId;
    }

    public Garage(String garageName, String garageCoordinatorPhone, String garageId, ArrayList<Product> garageProducts, ArrayList<Stock> garageStocks){
        this.garageProducts = garageProducts;
        this.garageStocks = garageStocks;
        this.garageName = garageName;
        this.garageCoordinatorPhone = garageCoordinatorPhone;
        this.garageId = garageId;
    }

    public Garage(String garageName, String garageCoordinatorPhone, String garageId, ArrayList<Product> garageProducts, ArrayList<Stock> garageStocks, ArrayList<Product> borrowedProducts){
        this.garageProducts = garageProducts;
        this.garageStocks = garageStocks;
        this.garageName = garageName;
        this.garageCoordinatorPhone = garageCoordinatorPhone;
        this.garageId = garageId;
        this.borrowedProducts = borrowedProducts;
    }

    public Garage(String garageName, String garageCoordinatorPhone, String garageId, ArrayList<Product> garageProducts, ArrayList<Stock> garageStocks, ArrayList<Product> borrowedProducts, ArrayList<Product> damagedProducts, ArrayList<Product> missingProducts){
        this.garageProducts = garageProducts;
        this.garageStocks = garageStocks;
        this.garageName = garageName;
        this.garageCoordinatorPhone = garageCoordinatorPhone;
        this.garageId = garageId;
        this.borrowedProducts = borrowedProducts;
        this.damagedProducts = damagedProducts;
        this.missingProducts = missingProducts;
    }
}

Firebase:

{
  "173baaa74c0" : {
    "garageCoordinatorPhone" : "0523122548",
    "garageId" : "173baaa74c0",
    "garageName" : "רעננה מרכז",
    "garageProducts" : [ {
      "description" : "אורך 1.7 מטר",
      "productAmount" : 5,
      "productCategory" : "בנייה מחנאית",
      "productId" : 201,
      "productName" : "בזנט"
    }, {
      "description" : "נפח 500 סמ'ק",
      "productAmount" : 5,
      "productCategory" : "כיבוי אש",
      "productId" : 402,
      "productName" : "מטפים תקינים"
    }, {
      "description" : "אורך 30 ס'מ",
      "productAmount" : 4,
      "productCategory" : "כלי עבודה",
      "productId" : 506,
      "productName" : "שפכטל"
    }, {
      "description" : "אורך 30 ס'מ",
      "productAmount" : 1,
      "productCategory" : "חשמל",
      "productId" : 323,
      "productName" : "DI"
    }, {
      "description" : "סיר מתכת לטיולים, קוטר 15 ס'מ",
      "productAmount" : 7,
      "productCategory" : "בישול",
      "productId" : 127,
      "productName" : "סיר בינוני"
    }, {
      "description" : "",
      "productAmount" : 1,
      "productCategory" : "חשמל",
      "productId" : 309,
      "productName" : "מיקרופון"
    } ],
    "garageStocks" : {
      "1610831472776" : {
        "stockFillerPhone" : "0544926410",
        "stockId" : 1610831472776,
        "stockProducts" : [ {
          "description" : "אורך 1.7 מטר",
          "productAmount" : 5,
          "productCategory" : "בנייה מחנאית",
          "productId" : 201,
          "productName" : "בזנט"
        }, {
          "description" : "נפח 500 סמ'ק",
          "productAmount" : 5,
          "productCategory" : "כיבוי אש",
          "productId" : 402,
          "productName" : "מטפים תקינים"
        }, {
          "description" : "אורך 30 ס'מ",
          "productAmount" : 4,
          "productCategory" : "כלי עבודה",
          "productId" : 506,
          "productName" : "שפכטל"
        }, {
          "description" : "אורך 30 ס'מ",
          "productAmount" : 1,
          "productCategory" : "חשמל",
          "productId" : 323,
          "productName" : "DI"
        }, {
          "description" : "סיר מתכת לטיולים, קוטר 15 ס'מ",
          "productAmount" : 7,
          "productCategory" : "בישול",
          "productId" : 127,
          "productName" : "סיר בינוני"
        }, {
          "description" : "",
          "productAmount" : 1,
          "productCategory" : "חשמל",
          "productId" : 309,
          "productName" : "מיקרופון"
        } ]
      }
    }
  },
  "1740c8d4920" : {
    "garageCoordinatorPhone" : "0544926411",
    "garageId" : "1740c8d4920",
    "garageName" : "אשדוד ט'ו",
    "garageProducts" : [ {
      "description" : "",
      "productAmount" : 2,
      "productCategory" : "שונות",
      "productHome" : "173baaa74c0",
      "productId" : 1102,
      "productName" : "דרבוקות גדולות"
    }, {
      "description" : "נפח 500 סמ'ק",
      "productAmount" : 2,
      "productCategory" : "כיבוי אש",
      "productHome" : "173baaa74c0",
      "productId" : 402,
      "productName" : "מטפים תקינים"
    } ]
  },
  "174534895e0" : {
    "borrowedProducts" : {
      "5f66189e 207aeaca" : [ {
        "description" : "סיר מתכת לטיולים, קוטר 15 ס'מ",
        "productAmount" : 1,
        "productCategory" : "בישול",
        "productHome" : "173baaa74c0",
        "productId" : 127,
        "productName" : "סיר בינוני"
      } ]
    },
    "garageCoordinatorPhone" : "0544926410",
    "garageId" : "174534895e0",
    "garageName" : "הכפתור",
    "garageProducts" : [ {
      "description" : "אורך 1.7 מטר",
      "productAmount" : 23,
      "productCategory" : "בנייה מחנאית",
      "productHome" : "173baaa74c0",
      "productId" : 201,
      "productName" : "בזנט"
    }, {
      "description" : "",
      "productAmount" : 2,
      "productCategory" : "שונות",
      "productHome" : "173baaa74c0",
      "productId" : 1102,
      "productName" : "דרבוקות גדולות"
    }, {
      "description" : "נפח 500 סמ'ק",
      "productAmount" : 1,
      "productCategory" : "כיבוי אש",
      "productHome" : "173baaa74c0",
      "productId" : 402,
      "productName" : "מטפים תקינים"
    } ]
  }
}

enter code here
shlomi
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    Upload the whole garage Activity for better reference – Karunesh Palekar Jan 18 '21 at 13:13
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    You've included a picture of the JSON tree in your question. Please replace that with the actual JSON as text, which you can easily get by clicking the Export JSON link in the overflow menu (⠇) of [your Firebase Database console](https://console.firebase.google.com/project/_/database/data/). Having the JSON as text makes it searchable, allows us to easily use it to test with your actual data and use it in our answer and in general is just a Good Thing to do. – Frank van Puffelen Jan 18 '21 at 16:25

2 Answers2

2

Based on your Firebase JSON, it looks like you're storing an object with fields for each Stock in garageStocks instead of a list like your Garage class expects.

For example, you have:

"garageStocks" : {
  "stockObject1": { ... },
  "stockObject2": { ... },
  ...
}

However, your Garage class expects a list: private ArrayList<Stock> garageStocks;, which should be the following in JSON:

"garageStocks": [
  { stock object 1 },
  { stock object 2 },
  ...
]

That's why you're getting the error that it expects a list and is getting a map instead.

To fix this, you have a couple of options:

  1. Change the way you push data to Firebase to make sure you're pushing a list
  2. Change the type of garageStocks to a HashMap

I don't know what you're currently doing for option 1, but you seem to be doing the correct thing for the product lists (ArrayList<Product>) in the Garage class, so that could be a good place to look.

Hope this helps!

kungpaogao
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  • The suggestion for looking at how I did at the case of ```ArrayList``` was helpful! I changed it so the code pushes a list instead of anything else! – shlomi Jan 18 '21 at 21:58
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the problem persists even if you change the hashmap to list. explanation: if on item of list is removed the realtime database reconsider the list as a hashmap and then throws the error. so I think this is a problem of firebase and need to be recovered by their team!

Miftah Classifieds
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