Package database provides the Database interface. All database drivers must implement this interface, register themselves, optionally provide a `WithInstance` function and pass the tests in package database/testing.
package database

import (
	
	
	

	iurl 
)

var (
	ErrLocked = fmt.Errorf("can't acquire lock")
)

const NilVersion int = -1

var driversMu sync.RWMutex
var drivers = make(map[string]Driver)
Driver is the interface every database driver must implement. How to implement a database driver? 1. Implement this interface. 2. Optionally, add a function named `WithInstance`. This function should accept an existing DB instance and a Config{} struct and return a driver instance. 3. Add a test that calls database/testing.go:Test() 4. Add own tests for Open(), WithInstance() (when provided) and Close(). All other functions are tested by tests in database/testing. Saves you some time and makes sure all database drivers behave the same way. 5. Call Register in init(). 6. Create a migrate/cli/build_<driver-name>.go file 7. Add driver name in 'DATABASE' variable in Makefile Guidelines: * Don't try to correct user input. Don't assume things. When in doubt, return an error and explain the situation to the user. * All configuration input must come from the URL string in func Open() or the Config{} struct in WithInstance. Don't os.Getenv().
Open returns a new driver instance configured with parameters coming from the URL string. Migrate will call this function only once per instance.
	Open(url string) (Driver, error)
Close closes the underlying database instance managed by the driver. Migrate will call this function only once per instance.
	Close() error
Lock should acquire a database lock so that only one migration process can run at a time. Migrate will call this function before Run is called. If the implementation can't provide this functionality, return nil. Return database.ErrLocked if database is already locked.
	Lock() error
Unlock should release the lock. Migrate will call this function after all migrations have been run.
	Unlock() error
Run applies a migration to the database. migration is garantueed to be not nil.
	Run(migration io.Reader) error
SetVersion saves version and dirty state. Migrate will call this function before and after each call to Run. version must be >= -1. -1 means NilVersion.
	SetVersion(version int, dirty bool) error
Version returns the currently active version and if the database is dirty. When no migration has been applied, it must return version -1. Dirty means, a previous migration failed and user interaction is required.
	Version() (version int, dirty bool, err error)
Drop deletes everything in the database. Note that this is a breaking action, a new call to Open() is necessary to ensure subsequent calls work as expected.
	Drop() error
}
Open returns a new driver instance.
func ( string) (Driver, error) {
	,  := iurl.SchemeFromURL()
	if  != nil {
		return nil, 
	}

	driversMu.RLock()
	,  := drivers[]
	driversMu.RUnlock()
	if ! {
		return nil, fmt.Errorf("database driver: unknown driver %v (forgotten import?)", )
	}

	return .Open()
}
Register globally registers a driver.
func ( string,  Driver) {
	driversMu.Lock()
	defer driversMu.Unlock()
	if  == nil {
		panic("Register driver is nil")
	}
	if ,  := drivers[];  {
		panic("Register called twice for driver " + )
	}
	drivers[] = 
}
List lists the registered drivers
func () []string {
	driversMu.RLock()
	defer driversMu.RUnlock()
	 := make([]string, 0, len(drivers))
	for  := range drivers {
		 = append(, )
	}
	return