I hesitate to call gorp an ORM. Go doesn‘t really have objects, at least not in the classic Smalltalk/Java sense. There goes the “O”. gorp doesn’t know anything about the relationships between your structs (at least not yet). So the “R” is questionable too (but I use it in the name because, well, it seemed more clever).
The “M” is alive and well. Given some Go structs and a database, gorp should remove a fair amount of boilerplate busy-work from your code.
I hope that gorp saves you time, minimizes the drudgery of getting data in and out of your database, and helps your code focus on algorithms, not infrastructure.
# install the library:
go get gopkg.in/gorp.v1
// use in your .go code:
import (
"gopkg.in/gorp.v1"
)
This project provides a stable release (v1.x tags) and a bleeding edge codebase (master).
gopkg.in/gorp.v1 points to the latest v1.x tag. The API‘s for v1 are stable and shouldn’t change. Development takes place at the master branch. Althought the code in master should always compile and test successfully, it might break API‘s. We aim to maintain backwards compatibility, but API’s and behaviour might be changed to fix a bug. Also note that API's that are new in the master branch can change until released as v2.
If you want to use bleeding edge, use github.com/go-gorp/gorp as import path.
Full godoc output from the latest v1 release is available here:
https://godoc.org/gopkg.in/gorp.v1
For the latest code in master:
https://godoc.org/github.com/go-gorp/gorp
This package is compatible with the last 2 major versions of Go, at this time 1.3 and 1.4.
Any earlier versions are only supported on a best effort basis and can be dropped any time. Go has a great compatibility promise. Upgrading your program to a newer version of Go should never really be a problem.
package main import ( "database/sql" "gopkg.in/gorp.v1" _ "github.com/mattn/go-sqlite3" "log" "time" ) func main() { // initialize the DbMap dbmap := initDb() defer dbmap.Db.Close() // delete any existing rows err := dbmap.TruncateTables() checkErr(err, "TruncateTables failed") // create two posts p1 := newPost("Go 1.1 released!", "Lorem ipsum lorem ipsum") p2 := newPost("Go 1.2 released!", "Lorem ipsum lorem ipsum") // insert rows - auto increment PKs will be set properly after the insert err = dbmap.Insert(&p1, &p2) checkErr(err, "Insert failed") // use convenience SelectInt count, err := dbmap.SelectInt("select count(*) from posts") checkErr(err, "select count(*) failed") log.Println("Rows after inserting:", count) // update a row p2.Title = "Go 1.2 is better than ever" count, err = dbmap.Update(&p2) checkErr(err, "Update failed") log.Println("Rows updated:", count) // fetch one row - note use of "post_id" instead of "Id" since column is aliased // // Postgres users should use $1 instead of ? placeholders // See 'Known Issues' below // err = dbmap.SelectOne(&p2, "select * from posts where post_id=?", p2.Id) checkErr(err, "SelectOne failed") log.Println("p2 row:", p2) // fetch all rows var posts []Post _, err = dbmap.Select(&posts, "select * from posts order by post_id") checkErr(err, "Select failed") log.Println("All rows:") for x, p := range posts { log.Printf(" %d: %v\n", x, p) } // delete row by PK count, err = dbmap.Delete(&p1) checkErr(err, "Delete failed") log.Println("Rows deleted:", count) // delete row manually via Exec _, err = dbmap.Exec("delete from posts where post_id=?", p2.Id) checkErr(err, "Exec failed") // confirm count is zero count, err = dbmap.SelectInt("select count(*) from posts") checkErr(err, "select count(*) failed") log.Println("Row count - should be zero:", count) log.Println("Done!") } type Post struct { // db tag lets you specify the column name if it differs from the struct field Id int64 `db:"post_id"` Created int64 Title string Body string } func newPost(title, body string) Post { return Post{ Created: time.Now().UnixNano(), Title: title, Body: body, } } func initDb() *gorp.DbMap { // connect to db using standard Go database/sql API // use whatever database/sql driver you wish db, err := sql.Open("sqlite3", "/tmp/post_db.bin") checkErr(err, "sql.Open failed") // construct a gorp DbMap dbmap := &gorp.DbMap{Db: db, Dialect: gorp.SqliteDialect{}} // add a table, setting the table name to 'posts' and // specifying that the Id property is an auto incrementing PK dbmap.AddTableWithName(Post{}, "posts").SetKeys(true, "Id") // create the table. in a production system you'd generally // use a migration tool, or create the tables via scripts err = dbmap.CreateTablesIfNotExists() checkErr(err, "Create tables failed") return dbmap } func checkErr(err error, msg string) { if err != nil { log.Fatalln(msg, err) } }
First define some types:
type Invoice struct { Id int64 Created int64 Updated int64 Memo string PersonId int64 } type Person struct { Id int64 Created int64 Updated int64 FName string LName string } // Example of using tags to alias fields to column names // The 'db' value is the column name // // A hyphen will cause gorp to skip this field, similar to the // Go json package. // // This is equivalent to using the ColMap methods: // // table := dbmap.AddTableWithName(Product{}, "product") // table.ColMap("Id").Rename("product_id") // table.ColMap("Price").Rename("unit_price") // table.ColMap("IgnoreMe").SetTransient(true) // type Product struct { Id int64 `db:"product_id"` Price int64 `db:"unit_price"` IgnoreMe string `db:"-"` }
Then create a mapper, typically you'd do this one time at app startup:
// connect to db using standard Go database/sql API // use whatever database/sql driver you wish db, err := sql.Open("mymysql", "tcp:localhost:3306*mydb/myuser/mypassword") // construct a gorp DbMap dbmap := &gorp.DbMap{Db: db, Dialect: gorp.MySQLDialect{"InnoDB", "UTF8"}} // register the structs you wish to use with gorp // you can also use the shorter dbmap.AddTable() if you // don't want to override the table name // // SetKeys(true) means we have a auto increment primary key, which // will get automatically bound to your struct post-insert // t1 := dbmap.AddTableWithName(Invoice{}, "invoice_test").SetKeys(true, "Id") t2 := dbmap.AddTableWithName(Person{}, "person_test").SetKeys(true, "Id") t3 := dbmap.AddTableWithName(Product{}, "product_test").SetKeys(true, "Id")
gorp supports embedding structs. For example:
type Names struct {
FirstName string
LastName string
}
type WithEmbeddedStruct struct {
Id int64
Names
}
es := &WithEmbeddedStruct{-1, Names{FirstName: "Alice", LastName: "Smith"}}
err := dbmap.Insert(es)
See the TestWithEmbeddedStruct function in gorp_test.go for a full example.
Automatically create / drop registered tables. This is useful for unit tests but is entirely optional. You can of course use gorp with tables created manually, or with a separate migration tool (like goose or migrate).
// create all registered tables dbmap.CreateTables() // same as above, but uses "if not exists" clause to skip tables that are // already defined dbmap.CreateTablesIfNotExists() // drop dbmap.DropTables()
Optionally you can pass in a logger to trace all SQL statements. I recommend enabling this initially while you're getting the feel for what gorp is doing on your behalf.
Gorp defines a GorpLogger interface that Go's built in log.Logger satisfies. However, you can write your own GorpLogger implementation, or use a package such as glog if you want more control over how statements are logged.
// Will log all SQL statements + args as they are run // The first arg is a string prefix to prepend to all log messages dbmap.TraceOn("[gorp]", log.New(os.Stdout, "myapp:", log.Lmicroseconds)) // Turn off tracing dbmap.TraceOff()
// Must declare as pointers so optional callback hooks // can operate on your data, not copies inv1 := &Invoice{0, 100, 200, "first order", 0} inv2 := &Invoice{0, 100, 200, "second order", 0} // Insert your rows err := dbmap.Insert(inv1, inv2) // Because we called SetKeys(true) on Invoice, the Id field // will be populated after the Insert() automatically fmt.Printf("inv1.Id=%d inv2.Id=%d\n", inv1.Id, inv2.Id)
Continuing the above example, use the Update method to modify an Invoice:
// count is the # of rows updated, which should be 1 in this example count, err := dbmap.Update(inv1)
If you have primary key(s) defined for a struct, you can use the Delete method to remove rows:
count, err := dbmap.Delete(inv1)
Use the Get method to fetch a single row by primary key. It returns nil if no row is found.
// fetch Invoice with Id=99 obj, err := dbmap.Get(Invoice{}, 99) inv := obj.(*Invoice)
Select() and SelectOne() provide a simple way to bind arbitrary queries to a slice or a single struct.
// Select a slice - first return value is not needed when a slice pointer is passed to Select() var posts []Post _, err := dbmap.Select(&posts, "select * from post order by id") // You can also use primitive types var ids []string _, err := dbmap.Select(&ids, "select id from post") // Select a single row. // Returns an error if no row found, or if more than one row is found var post Post err := dbmap.SelectOne(&post, "select * from post where id=?", id)
Want to do joins? Just write the SQL and the struct. gorp will bind them:
// Define a type for your join // It *must* contain all the columns in your SELECT statement // // The names here should match the aliased column names you specify // in your SQL - no additional binding work required. simple. // type InvoicePersonView struct { InvoiceId int64 PersonId int64 Memo string FName string } // Create some rows p1 := &Person{0, 0, 0, "bob", "smith"} dbmap.Insert(p1) // notice how we can wire up p1.Id to the invoice easily inv1 := &Invoice{0, 0, 0, "xmas order", p1.Id} dbmap.Insert(inv1) // Run your query query := "select i.Id InvoiceId, p.Id PersonId, i.Memo, p.FName " + "from invoice_test i, person_test p " + "where i.PersonId = p.Id" // pass a slice to Select() var list []InvoicePersonView _, err := dbmap.Select(&list, query) // this should test true expected := InvoicePersonView{inv1.Id, p1.Id, inv1.Memo, p1.FName} if reflect.DeepEqual(list[0], expected) { fmt.Println("Woot! My join worked!") }
gorp provides a few convenience methods for selecting a single string or int64.
// select single int64 from db (use $1 instead of ? for postgresql) i64, err := dbmap.SelectInt("select count(*) from foo where blah=?", blahVal) // select single string from db: s, err := dbmap.SelectStr("select name from foo where blah=?", blahVal)
You may use a map or struct to bind parameters by name. This is currently only supported in SELECT queries.
_, err := dbm.Select(&dest, "select * from Foo where name = :name and age = :age", map[string]interface{}{
"name": "Rob",
"age": 31,
})
You can execute raw SQL if you wish. Particularly good for batch operations.
res, err := dbmap.Exec("delete from invoice_test where PersonId=?", 10)
You can batch operations into a transaction:
func InsertInv(dbmap *DbMap, inv *Invoice, per *Person) error { // Start a new transaction trans, err := dbmap.Begin() if err != nil { return err } trans.Insert(per) inv.PersonId = per.Id trans.Insert(inv) // if the commit is successful, a nil error is returned return trans.Commit() }
Use hooks to update data before/after saving to the db. Good for timestamps:
// implement the PreInsert and PreUpdate hooks func (i *Invoice) PreInsert(s gorp.SqlExecutor) error { i.Created = time.Now().UnixNano() i.Updated = i.Created return nil } func (i *Invoice) PreUpdate(s gorp.SqlExecutor) error { i.Updated = time.Now().UnixNano() return nil } // You can use the SqlExecutor to cascade additional SQL // Take care to avoid cycles. gorp won't prevent them. // // Here's an example of a cascading delete // func (p *Person) PreDelete(s gorp.SqlExecutor) error { query := "delete from invoice_test where PersonId=?" err := s.Exec(query, p.Id); if err != nil { return err } return nil }
Full list of hooks that you can implement:
PostGet PreInsert PostInsert PreUpdate PostUpdate PreDelete PostDelete All have the same signature. for example: func (p *MyStruct) PostUpdate(s gorp.SqlExecutor) error
gorp provides a simple optimistic locking feature, similar to Java's JPA, that will raise an error if you try to update/delete a row whose version column has a value different than the one in memory. This provides a safe way to do “select then update” style operations without explicit read and write locks.
// Version is an auto-incremented number, managed by gorp // If this property is present on your struct, update // operations will be constrained // // For example, say we defined Person as: type Person struct { Id int64 Created int64 Updated int64 FName string LName string // automatically used as the Version col // use table.SetVersionCol("columnName") to map a different // struct field as the version field Version int64 } p1 := &Person{0, 0, 0, "Bob", "Smith", 0} dbmap.Insert(p1) // Version is now 1 obj, err := dbmap.Get(Person{}, p1.Id) p2 := obj.(*Person) p2.LName = "Edwards" dbmap.Update(p2) // Version is now 2 p1.LName = "Howard" // Raises error because p1.Version == 1, which is out of date count, err := dbmap.Update(p1) _, ok := err.(gorp.OptimisticLockError) if ok { // should reach this statement // in a real app you might reload the row and retry, or // you might propegate this to the user, depending on the desired // semantics fmt.Printf("Tried to update row with stale data: %v\n", err) } else { // some other db error occurred - log or return up the stack fmt.Printf("Unknown db err: %v\n", err) }
gorp uses the Go 1 database/sql package. A full list of compliant drivers is available here:
http://code.google.com/p/go-wiki/wiki/SQLDrivers
Sadly, SQL databases differ on various issues. gorp provides a Dialect interface that should be implemented per database vendor. Dialects are provided for:
Each of these three databases pass the test suite. See gorp_test.go for example DSNs for these three databases.
Support is also provided for:
Note that these databases are not covered by CI and I (@coopernurse) have no good way to test them locally. So please try them and send patches as needed, but expect a bit more unpredicability.
Different databases use different strings to indicate variable placeholders in prepared SQL statements. Unlike some database abstraction layers (such as JDBC), Go's database/sql does not standardize this.
SQL generated by gorp in the Insert, Update, Delete, and Get methods delegates to a Dialect implementation for each database, and will generate portable SQL.
Raw SQL strings passed to Exec, Select, SelectOne, SelectInt, etc will not be parsed. Consequently you may have portability issues if you write a query like this:
// works on MySQL and Sqlite3, but not with Postgresql err := dbmap.SelectOne(&val, "select * from foo where id = ?", 30)
In Select and SelectOne you can use named parameters to work around this. The following is portable:
err := dbmap.SelectOne(&val, "select * from foo where id = :id",
map[string]interface{} { "id": 30})
gorp will pass time.Time fields through to the database/sql driver, but note that the behavior of this type varies across database drivers.
MySQL users should be especially cautious. See: https://github.com/ziutek/mymysql/pull/77
To avoid any potential issues with timezone/DST, consider using an integer field for time data and storing UNIX time.
The included tests may be run against MySQL, Postgresql, or sqlite3. You must set two environment variables so the test code knows which driver to use, and how to connect to your database.
# MySQL example: export GORP_TEST_DSN=gomysql_test/gomysql_test/abc123 export GORP_TEST_DIALECT=mysql # run the tests go test # run the tests and benchmarks go test -bench="Bench" -benchtime 10
Valid GORP_TEST_DIALECT values are: “mysql”(for mymysql), “gomysql”(for go-sql-driver), “postgres”, “sqlite” See the test_all.sh script for examples of all 3 databases. This is the script I run locally to test the library.
gorp uses reflection to construct SQL queries and bind parameters. See the BenchmarkNativeCrud vs BenchmarkGorpCrud in gorp_test.go for a simple perf test. On my MacBook Pro gorp is about 2-3% slower than hand written SQL.
Automatic mapping of the version column used in optimistic locking has been removed as it could cause problems if the type was not int. The version column must now explicitly be set with tablemap.SetVersionCol().
IRC: #gorp Mailing list: gorp-dev@googlegroups.com Bugs/Enhancements: Create a github issue
Contributions are very welcome. Please follow these guidelines:
master branch and issue pull requests targeting the master branchThanks!