How to deal with unknown variables or How to deal with multiple databases

go

Solution

If you want to preserve the interface with those methods, you should change a little your interface as:

Interface:

// The interface that all connectors should have
type Intfc interface {
    // Connect to the database, if an error occur at the moment
    // of connection, return the error
    Connect() error
    // Add returns a string, it returns an error if something occurs
    Add(string, string, string) (string, error)
    Get(string) (Object, bool)
}

MySQL:

type Mysql struct{
    conn *sql.DB // contains the connection to the DB
}

// Connect to mysql
func (f *Mysql) Connect() error {
    conn, err := sql.Open("mysql", "yourusername:yourpassword@/yourdatabase")
    if err != nil {
        return error
    }
    f.conn = conn
    return nil
}

// Add item to DB
func (f *Mysql) Add(owner string, refType string, object string) (string, error) {
    // do something
    return // a string and error
}

func (f *Mysql) Get(Uuid string) (dbinit.Object, bool) {
    // do something
    return // an object and a bool
}

Mongo:

type Mongo struct{
    session *mgo.Session
}

// Connect to mongo
func (f *Mongo) Connect() error {
    info := &mgo.DialInfo{
        // some data
    }

    session, err := mgo.DialWithInfo(info)
    if err != nil {
        return error
    }
    f.session = session
    return nil
}

// Add item to DB
func (f *Mongo) Add(owner string, refType string, object string) (string, error) {
    // do something
    return // a string and error (it could be nil at success)
}

func (f *Mongo) Get(Uuid string) (dbinit.Object, bool) {
    // do something
    return // an object and a bool
}

Main:

var selectedDb dbinit.Intfc

commandLineInput := "mysql"

if commandLineInput == "mysql" {
    selectedDb = &mysqlConnector.Mysql{}
} else if commandLineInput == "mongo" {
    selectedDb = &mongoConnector.Mongo{}
}

err := selectedDb.Connect()
if err != nil {
    panic(err)
}

// this runs everytime the API is called
api.HandlerFoobar = foobar.handlerFunction(func(params foobar.Params) middleware.Responder {
    data, err := selectedDb.Add(addStringA, addStringB, addStringC)
    if err != nil {
        // do something
    }

    return // the API response
})

But you also can remove the `Connect() error` method from `Intfc` and just use `Add` and `Get`, but you should update the packages like:

Mysql

// Connect to mysql, it could be any function name
func Connect() (*Mysql, error) {
    connection, err := sql.Open("mysql", "yourusername:yourpassword@/yourdatabase")
    if err != nil {
        return nil, error
    }
    return &Mysql{conn: connection}
}

Mongo

// Connect to mongo, it could be any function name
func Connect() (*Mongo, error) {
    info := &mgo.DialInfo{
        // some data
    }

    s, err := mgo.DialWithInfo(info)
    if err != nil {
        return nil, error
    }
    return &Mongo{session: s}
}

Main

var selectedDb dbinit.Intfc
var err error
commandLineInput := "mysql"

if commandLineInput == "mysql" {
    selectedDb, err = mysqlConnector.Connect()
} else if commandLineInput == "mongo" {
    selectedDb, err = mongoConnector.Connect()
}

if err != nil {
    panic(err)
}

Problem

Original source