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driver.go
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driver.go
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// Package database provides the Driver 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 (
"fmt"
"io"
"sync"
iurl "github.com/dendy1/migrate/v4/internal/url"
)
var (
ErrLocked = fmt.Errorf("can't acquire lock")
ErrNotLocked = fmt.Errorf("can't unlock, as not currently locked")
)
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 internal/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().
type Driver interface {
// 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 guaranteed 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 Open(url string) (Driver, error) {
scheme, err := iurl.SchemeFromURL(url)
if err != nil {
return nil, err
}
driversMu.RLock()
d, ok := drivers[scheme]
driversMu.RUnlock()
if !ok {
return nil, fmt.Errorf("database driver: unknown driver %v (forgotten import?)", scheme)
}
return d.Open(url)
}
// Register globally registers a driver.
func Register(name string, driver Driver) {
driversMu.Lock()
defer driversMu.Unlock()
if driver == nil {
panic("Register driver is nil")
}
if _, dup := drivers[name]; dup {
panic("Register called twice for driver " + name)
}
drivers[name] = driver
}
// List lists the registered drivers
func List() []string {
driversMu.RLock()
defer driversMu.RUnlock()
names := make([]string, 0, len(drivers))
for n := range drivers {
names = append(names, n)
}
return names
}