Firebase实时数据库读取报错：无法将String转为Cartmodel

错误信息 #

com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String to type com.example.register.Model.Cartmodel

写入数据代码 #

private void addtocart() {
    String saveCurrentDate, saveCurrentTime;
    Calendar calForDate = Calendar.getInstance();
    SimpleDateFormat currentDate = new SimpleDateFormat("MMM dd, yyyy");
    saveCurrentDate = currentDate.format(calForDate.getTime());

    SimpleDateFormat currentTime = new SimpleDateFormat("HH:mm:ss a");
    saveCurrentTime = currentTime.format(calForDate.getTime());

    final DatabaseReference cartListRef = FirebaseDatabase.getInstance().getReference().child("Cart List");
    String timestamp = String.valueOf(System.currentTimeMillis());

    double price = Double.parseDouble(emailholder.getText().toString().replace("₹", ""));
    double quantityValue = Double.parseDouble(quantity.getText().toString());
    double result = price * quantityValue;

    Intent intent = getIntent();
    String purl = intent.getStringExtra("purl");

    final HashMap<String, Object> cartMap = new HashMap<>();
    cartMap.put("productName",nameholder.getText().toString());
    cartMap.put("productPrice",emailholder.getText().toString());
    cartMap.put("productImage", purl);
    cartMap.put("date",saveCurrentDate);
    cartMap.put("time",saveCurrentTime);
    cartMap.put("quantity",quantity.getText().toString());
    cartMap.put("totalPrice",result);

    String currentUserPhoneNumber = Paper.book().read(Prevalent.UserPhoneKey);

    cartListRef.child("currentUserPhoneNumber")
            //.child(timestamp)
            .updateChildren(cartMap)
            .addOnCompleteListener(new OnCompleteListener<Void>() {
                @Override
                public void onComplete(@NonNull Task<Void> task) {
                    Toast.makeText(details.this, "Added to cart", Toast.LENGTH_SHORT).show();
                }
            });
}

Model类代码 #

package com.example.register.Model;

public class Cartmodel {
    String date;
    String productImage;
    static String productName;
    String productPrice;
    static String quantity;
    String time;
    static String totalPrice;

    public Cartmodel() {
    }

    public Cartmodel(String date, String productImage, String productName, String quantity, String time, String totalPrice,String productPrice) {
        this.date = date;
        this.productImage = productImage;
        this.productName = productName;
        this.quantity = quantity;
        this.time = time;
        this.totalPrice = totalPrice;
        this.productPrice = productPrice;
    }

    public String getProductPrice() {
        return productPrice;
    }

    public void setProductPrice(String productPrice) {
        this.productPrice = productPrice;
    }

    public String getDate() {
        return date;
    }

    public void setDate(String date) {
        this.date = date;
    }

    public String getProductImage() {
        return productImage;
    }

    public void setProductImage(String productImage) {
        this.productImage = productImage;
    }

    public static String getProductName() {
        return productName;
    }

    public void setProductName(String productName) {
        this.productName = productName;
    }

    public static String getQuantity() {
        return quantity;
    }

    public void setQuantity(String quantity) {
        this.quantity = quantity;
    }

    public String getTime() {
        return time;
    }

    public void setTime(String time) {
        this.time = time;
    }

    public static String getTotalPrice() {
        return totalPrice;
    }

    public void setTotalPrice(String totalPrice) {
        this.totalPrice = totalPrice;
    }
}

读取数据代码 #

@Override
protected void onStart() {
    super.onStart();
    String currentUserPhoneNumber = Paper.book().read(UserPhoneKey);
    String timestamp = String.valueOf(System.currentTimeMillis());

    final DatabaseReference cartListRef = FirebaseDatabase.getInstance().getReference().child("Cart List");

    FirebaseRecyclerOptions<Cartmodel> options =
            new FirebaseRecyclerOptions.Builder<Cartmodel>()
                    .setQuery(cartListRef.child("currentUserPhoneNumber")
                            /**.child(timestamp)**/,Cartmodel.class).build();

    FirebaseRecyclerAdapter<Cartmodel, CartViewHolder> adapter
            =new FirebaseRecyclerAdapter<Cartmodel, CartViewHolder>(options) {
        @Override
        protected void onBindViewHolder(@NonNull CartViewHolder holder, int position, @NonNull Cartmodel model) {
            holder.TxtQunatity.setText(Cartmodel.getQuantity());
            holder.TxtProductPrice.setText(Cartmodel.getProductName());
            holder.TxtProductName.setText(Cartmodel.getTotalPrice());
        }

        @NonNull
        @Override
        public CartViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
            View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.cart_row,parent,false);
            CartViewHolder holder = new CartViewHolder(view);
            return holder;
        }
    };

    recyclerView.setAdapter(adapter);
    adapter.startListening();
}

数据库结构 #

"Cart List": {
  "currentUserPhoneNumber": {
    "date": "Feb 15, 2023",
    "productImage": "https://images.jdmagicbox.com/comp/mumbai/z3/022pxx22.xx22.181204184809.b5z3/catalogue/burger-king-santacruz-east-mumbai-burger-king-3hofjz4vmz.jpg",
    "productName": "Chicken Burger",
    "productPrice": "₹₹350",
    "quantity": "3",
    "time": "15:08:00 PM",
    "totalPrice": 1050
  }
}

问题原因及解决方案 #

核心问题 #

1. 数据结构不匹配：数据库中currentUserPhoneNumber节点直接存储单个购物车项的字段，而FirebaseRecyclerAdapter期望查询的是多个Cartmodel对象的列表（每个子节点对应一个完整对象）。
2. Model类静态字段错误：productName、quantity、totalPrice被定义为静态字段，导致Gson无法正确映射实例数据，且所有实例共享同一值。
3. 读取逻辑错误：onBindViewHolder中调用静态方法获取字段，而非使用传入的model实例；同时查询路径未指向用户专属节点，且未匹配列表结构。
4. 数据类型不匹配：数据库中totalPrice是数字类型，但Model类中定义为String类型，解析时会报错。

修复步骤 #

1. 修正Model类，移除静态字段并统一数据类型

package com.example.register.Model;

public class Cartmodel {
    String date;
    String productImage;
    String productName;
    String productPrice;
    String quantity;
    String time;
    double totalPrice;

    public Cartmodel() {
    }

    public Cartmodel(String date, String productImage, String productName, String quantity, String time, double totalPrice, String productPrice) {
        this.date = date;
        this.productImage = productImage;
        this.productName = productName;
        this.quantity = quantity;
        this.time = time;
        this.totalPrice = totalPrice;
        this.productPrice = productPrice;
    }

    public String getProductPrice() {
        return productPrice;
    }

    public void setProductPrice(String productPrice) {
        this.productPrice = productPrice;
    }

    public String getDate() {
        return date;
    }

    public void setDate(String date) {
        this.date = date;
    }

    public String getProductImage() {
        return productImage;
    }

    public void setProductImage(String productImage) {
        this.productImage = productImage;
    }

    public String getProductName() {
        return productName;
    }

    public void setProductName(String productName) {
        this.productName = productName;
    }

    public String getQuantity() {
        return quantity;
    }

    public void setQuantity(String quantity) {
        this.quantity = quantity;
    }

    public String getTime() {
        return time;
    }

    public void setTime(String time) {
        this.time = time;
    }

    public double getTotalPrice() {
        return totalPrice;
    }

    public void setTotalPrice(double totalPrice) {
        this.totalPrice = totalPrice;
    }
}

2. 修正写入数据的结构，区分用户并存储为列表形式

// 替换写入逻辑中的节点路径部分
cartListRef.child(currentUserPhoneNumber) // 使用变量存储用户手机号，而非固定字符串
        .child(timestamp) // 用timestamp作为每个购物车项的唯一标识
        .updateChildren(cartMap)
        .addOnCompleteListener(new OnCompleteListener<Void>() {
            @Override
            public void onComplete(@NonNull Task<Void> task) {
                Toast.makeText(details.this, "Added to cart", Toast.LENGTH_SHORT).show();
            }
        });

3. 修正读取数据的逻辑，匹配列表结构并使用实例字段

@Override
protected void onStart() {
    super.onStart();
    String currentUserPhoneNumber = Paper.book().read(UserPhoneKey);

    final DatabaseReference cartListRef = FirebaseDatabase.getInstance().getReference().child("Cart List");

    FirebaseRecyclerOptions<Cartmodel> options =
            new FirebaseRecyclerOptions.Builder<Cartmodel>()
                    // 查询用户节点下的所有购物车项子节点
                    .setQuery(cartListRef.child(currentUserPhoneNumber), Cartmodel.class).build();

    FirebaseRecyclerAdapter<Cartmodel, CartViewHolder> adapter
            =new FirebaseRecyclerAdapter<Cartmodel, CartViewHolder>(options) {
        @Override
        protected void onBindViewHolder(@NonNull CartViewHolder holder, int position, @NonNull Cartmodel model) {
            // 使用model实例的getter方法获取字段值
            holder.TxtQunatity.setText(model.getQuantity());
            holder.TxtProductPrice.setText(model.getProductPrice());
            holder.TxtProductName.setText(model.getProductName());
            // 如果需要显示总价，可转成字符串：String.valueOf(model.getTotalPrice())
        }

        @NonNull
        @Override
        public CartViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
            View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.cart_row,parent,false);
            CartViewHolder holder = new CartViewHolder(view);
            return holder;
        }
    };

    recyclerView.setAdapter(adapter);
    adapter.startListening();
}

内容的提问来源于stack exchange，提问作者Aditya Singh Rajput