Data validation rules in Firebase - Step-by-Step Execution

Process Flow - Data validation rules

Client sends data write request

↓

Firebase receives request

↓

Check validation rules

↓

Write data

↓

Confirm success

When a client tries to write data, Firebase checks the validation rules. If data is valid, it writes; if not, it rejects.

Execution Sample

Firebase

rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {
    match /users/{userId} {
      allow write: if request.resource.data.age >= 18;
    }
  }
}

This rule allows writing user data only if the age is 18 or older.

Process Table

Step	Action	Data Sent	Validation Check	Result
1	Client sends write request	{"age": 20}	Check if age >= 18	Valid - allow write
2	Write data to database	{"age": 20}	N/A	Write successful
3	Client sends write request	{"age": 16}	Check if age >= 18	Invalid - reject write
4	Reject write request	{"age": 16}	N/A	Write rejected with error

💡 Execution stops after write is allowed or rejected based on validation.

Status Tracker

Variable	Start	After Step 1	After Step 3	Final
request.resource.data.age	undefined	20	16	N/A
validation result	undefined	true	false	N/A

Key Moments - 2 Insights

Why does the write get rejected when age is 16?

Because the validation rule requires age to be 18 or older, as shown in execution_table step 3 where the check fails.

What happens if the data passes validation?

The data is written to the database successfully, as seen in execution_table step 2.

Visual Quiz - 3 Questions

Look at the execution table, what is the validation result when age is 20?

A No validation performed

B Invalid - reject write

C Valid - allow write

D Write rejected with error

💡 Hint

Check execution_table row 1 under 'Validation Check' and 'Result'

At which step does the write get rejected?

A Step 2

B Step 4

C Step 3

D Step 1

💡 Hint

Look at execution_table rows 3 and 4 for rejection details

If the rule changed to age >= 21, what would happen at step 1 with age 20?

A Write rejected

B No change

C Write allowed

D Error in rule

💡 Hint

Compare the validation condition in execution_sample with the data in execution_table

Concept Snapshot

Firebase Data Validation Rules:
- Define rules to check data before writing
- Use conditions like 'age >= 18'
- If data passes, write allowed
- If data fails, write rejected
- Protects database from bad data

Full Transcript

When a client tries to write data to Firebase, the system checks the data against validation rules. For example, a rule might require the user's age to be 18 or older. If the data meets this rule, Firebase writes it to the database and confirms success. If not, Firebase rejects the write and sends an error. This process ensures only valid data is stored.