Firebase Rules validation and catching validation fail in android application

Question

Design

• A user who can login to the application
• Logged in user can create customers which will be stored under node whose val

Answer 1

I think that you can insert up to 5 characters because your .length for your newData.val().lenght start at 0, like an array. In other way, if you want to link uniqueness of a customerCode for each userId you should create a new table in your firebase database, Something like:

{
  "customers": {
    "UserId1": {
      "custId1": {
        "customerCode": "customerId1",
        "customerLimit": "58866",
        "customerName": "Test New "
      },
      "custId2": {
        "customerCode": "customerId2",
        "customerLimit": "5698",
        "customerName": "Yeth"
      }
    },
    "UserId2": {
      "custId3": {
        "customerCode": "customerId3",
        "customerLimit": "5886",
        "customerName": "Test "
      },
      "custId4": {
        "customerCode": "customerId4",
        "customerLimit": "58669",
        "customerName": "New Test"
      }
    }
  }
  "customerCode": {
    "custId1": {
      "customerId1": "thh"
    }
    "custId2": {
      "customerId2": "thk"
    }
    "custId3": {
      "customerId3": "thh"
    }
    "custId4": {
      "customerId4": "tbh"
    }
  }
}

Using this model, you can modify your rules to so something like this:

{
  "rules": {
    "customers": {
      ".read": "auth != null",
      ".write": "auth != null",
      "$CID": {
        "customerName": {
          ".validate": "newData.isString() && newData.val().length < 100"
        },
        "customerCode": {
          //Code shouls be string, less than 4 characters and it can't be already stored on customerCode table for the current userId
          ".validate": "newData.isString() && newData.val().length<3  && !root.child('customerCode').child(auth.uid).exists()"
        },
        "customerLimit": {}
      }
    }
    "customerCode": {
      "$CID": {
        "CustomerCodeId": {
          ".read": "auth != null",
          ".write": "auth != null",
        }
      }
    }
  }

Maybe the rules are not perfect in the last example, but I'm sure that you can find the way about how it can fits in your app taking a look about firechat database rules. I learned a lot looking that repository.