Simplebank

A demo application build using Golang and Postgres.

This applciation is built during this course

Things I Learnt

• SQLC - A Golang package that generates typesafe code from SQL files.

  • Generated code is fast as it uses the standard libray only.
  • Checks SQL errors while generating the code
  • Generates json tags and a lot more

• Composition in Golang - Composition in golang is a way to "inherit" behaviour from other structs without actually having to implement subclasses and superclasses.

  • They act like member variables with some syntactic sugar on top.

  • You still can initializes the "composite members" like you would any member in the strcut, just with typename as field name

      // Here, `Store` struct gets behaviour from `Queries` struct 
      type Store struct {
        *Queries
        db *sql.DB
      }
    
      // `Queries` struct is initialized normally by using type name as the field name
      func NewStore(db *sql.DB) *Store {
        return &Store{
          db:      db,
          Queries: New(db),
        }
      }

• Database Transactions and Dealocks - Although I know about basics of database transactions, there is a lot I learnt about them and how they interact with problems like deadlocks.

  • A transaction has an isolation level defined (either globally or for a particular db session) which governs what it can see and what it can't see

  • These are implemented using different ways in different DB Engines to achieve similar results.

  • Deadlocks can occur when 2 transaction try to update / read the same data (depending on the isolation level) at the same time.

    • To handle this, I had to implement the addMoney method in store.go which is called with the smaller ID first. (see TransferTx)
    • The best way to deal with deadlocks is to avoid them

• JWT vs PASETO - I generally assumed that JWT works fine and wasn't aware of it's vulnerabilities. But I learnt that JWT is regarded as a poorly written standard and exposes security vulnerabilities. It seems there is common consensus that PASETO (Platform Agnostic SEecure TOkens- the newer standard for tokens) should be used.

Isolation Levels and Their behaviour in different DB Engines