Update User Details

#### User Story:
> Existing user can update their details.

#### Pre-requisites:
- [ ] User DAO (update)
- [ ] User Service (update)

#### Validations:

- [ ] Form Validation:
- Id <= 0
- User Object
- User null
- Name ( null, empty, pattern )
- Password ( null, empty, pattern )
- Phone number ( length, >= 600000001 && <= 9999999999 )

- [ ] Business Validation:
- Check whether the Id exists.

#### Messages:
- User Id cannot be less than zero.
- User object cannot be null.
- Name cannot be null or empty.
- Password cannot be null or empty.
- Password does not match the pattern.
- Phone number cannot be less than or more than 10 digits.
- Phone number does not match the pattern.
- Id doesn't exists.

#### Flow:

```mermaid
graph TD;
A(Value Passed to UserService - Id & User object) --> B(Form Validation) -- Valid --> C(Business Validation)
B --Invalid --> H(Validation Exception)
C -- Valid--> D(Value Passed to UserDAO)
D --> E(Update value from Database)
C -- Invalid --> F(Validation Exception)
```

Start by locating the UserService and UserDAO entry points named in the prerequisites and trace the update flow from the service to the database. Cover the listed form and business validation cases, then verify that valid details are persisted and invalid inputs produce the specified messages.

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