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Go Relational Persistence

Update 2016-11-13: Future versions

As many of the maintainers have become busy with other projects, progress toward the ever-elusive v2 has slowed to the point that we're only occasionally making progress outside of merging pull requests. In the interest of continuing to release, I'd like to lean toward a more maintainable path forward.

For the moment, I am releasing a v2 tag with the current feature set from master, as some of those features have been actively used and relied on by more than one project. Our next goal is to continue cleaning up the code base with non-breaking changes as much as possible, but if/when a breaking change is needed, we'll just release new versions. This allows us to continue development at whatever pace we're capable of, without delaying the release of features or refusing PRs.

Introduction

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.

Bind struct fields to table columns via API or tag
Support for embedded structs
Support for transactions
Forward engineer db schema from structs (great for unit tests)
Pre/post insert/update/delete hooks
Automatically generate insert/update/delete statements for a struct
Automatic binding of auto increment PKs back to struct after insert
Delete by primary key(s)
Select by primary key(s)
Optional trace sql logging
Bind arbitrary SQL queries to a struct
Bind slice to SELECT query results without type assertions
Use positional or named bind parameters in custom SELECT queries
Optional optimistic locking using a version column (for update/deletes)

Installation

Use go get or your favorite vendoring tool, using whichever import path you'd like.

Versioning

We use semantic version tags. Feel free to import through gopkg.in (e.g. gopkg.in/gorp.v2) to get the latest tag for a major version, or check out the tag using your favorite vendoring tool.

Development is not very active right now, but we have plans to restructure gorp as we continue to move toward a more extensible system. Whenever a breaking change is needed, the major version will be bumped.

The master branch is where all development is done, and breaking changes may happen from time to time. That said, if you want to live on the bleeding edge and are comfortable updating your code when we make a breaking change, you may use github.com/go-gorp/gorp as your import path.

Check the version tags to see what's available. We'll make a good faith effort to add badges for new versions, but we make no guarantees.

Supported Go versions

This package is guaranteed to be compatible with the latest 2 major versions of Go.

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.

Migration guide

Pre-v2 to v2

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().

Help/Support

Use our gitter channel. We used to use IRC, but with most of us being pulled in many directions, we often need the email notifications from gitter to yell at us to sign in.

Quickstart

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 `db:",size:50"`               // Column size set to 50
    Body    string `db:"article_body,size:1024"` // Set both column name and size
}

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)
    }
}

Examples

Mapping structs to tables

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)
//
// You can optionally declare the field to be a primary key and/or autoincrement
//
type Product struct {
    Id         int64     `db:"product_id, primarykey, autoincrement"`
    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")

Struct Embedding

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.

Create/Drop Tables

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 sql-migrate, 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()

SQL Logging

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()

Insert

// 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)

Update

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)

Delete

If you have primary key(s) defined for a struct, you can use the Delete method to remove rows:

count, err := dbmap.Delete(inv1)

Select by Key

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)

Ad Hoc SQL

SELECT

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"}
err = dbmap.Insert(p1)
checkErr(err, "Insert failed")

// notice how we can wire up p1.Id to the invoice easily
inv1 := &Invoice{0, 0, 0, "xmas order", p1.Id}
err = dbmap.Insert(inv1)
checkErr(err, "Insert failed")

// 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!")
}

SELECT string or int64

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)

Named bind parameters

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,
})

UPDATE / DELETE

You can execute raw SQL if you wish. Particularly good for batch operations.

res, err := dbmap.Exec("delete from invoice_test where PersonId=?", 10)

Transactions

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
    }

    err = trans.Insert(per)
    checkErr(err, "Insert failed")

    inv.PersonId = per.Id
    err = trans.Insert(inv)
    checkErr(err, "Insert failed")

    // if the commit is successful, a nil error is returned
    return trans.Commit()
}

Hooks

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

Optimistic Locking

Note that this behaviour has changed in v2. See Migration Guide.

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}
err = dbmap.Insert(p1)  // Version is now 1
checkErr(err, "Insert failed")

obj, err := dbmap.Get(Person{}, p1.Id)
p2 := obj.(*Person)
p2.LName = "Edwards"
_,err = dbmap.Update(p2)  // Version is now 2
checkErr(err, "Update failed")

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)
}

Adding INDEX(es) on column(s) beyond the primary key

Indexes are frequently critical for performance. Here is how to add them to your tables.

NB: SqlServer and Oracle need testing and possible adjustment to the CreateIndexSuffix() and DropIndexSuffix() methods to make AddIndex() work for them.

In the example below we put an index both on the Id field, and on the AcctId field.

type Account struct {
	Id      int64
	AcctId  string // e.g. this might be a long uuid for portability
}

// indexType (the 2nd param to AddIndex call) is "Btree" or "Hash" for MySQL.
// demonstrate adding a second index on AcctId, and constrain that field to have unique values.
dbm.AddTable(iptab.Account{}).SetKeys(true, "Id").AddIndex("AcctIdIndex", "Btree", []string{"AcctId"}).SetUnique(true)

err = dbm.CreateTablesIfNotExists()
checkErr(err, "CreateTablesIfNotExists failed")

err = dbm.CreateIndex()
checkErr(err, "CreateIndex failed")

Check the effect of the CreateIndex() call in mysql:

$ mysql

MariaDB [test]> show create table Account;
+---------+--------------------------+
| Account | CREATE TABLE `Account` (
  `Id` bigint(20) NOT NULL AUTO_INCREMENT,
  `AcctId` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`Id`),
  UNIQUE KEY `AcctIdIndex` (`AcctId`) USING BTREE   <<<--- yes! index added.
) ENGINE=InnoDB DEFAULT CHARSET=utf8 
+---------+--------------------------+

Database Drivers

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:

MySQL
PostgreSQL
sqlite3

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:

Oracle (contributed by @klaidliadon)
SQL Server (contributed by @qrawl) - use driver: github.com/denisenkom/go-mssqldb

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.

Sqlite3 Extensions

In order to use sqlite3 extensions you need to first register a custom driver:

import (
	"database/sql"

	// use whatever database/sql driver you wish
	sqlite "github.com/mattn/go-sqlite3"
)

func customDriver() (*sql.DB, error) {

	// create custom driver with extensions defined
	sql.Register("sqlite3-custom", &sqlite.SQLiteDriver{
		Extensions: []string{
			"mod_spatialite",
		},
	})

	// now you can then connect using the 'sqlite3-custom' driver instead of 'sqlite3'
	return sql.Open("sqlite3-custom", "/tmp/post_db.bin")
}

Known Issues

SQL placeholder portability

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})

Additionally, when using Postgres as your database, you should utilize $1 instead of ? placeholders as utilizing ? placeholders when querying Postgres will result in pq: operator does not exist errors. Alternatively, use dbMap.Dialect.BindVar(varIdx) to get the proper variable binding for your dialect.

time.Time and time zones

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.
Using a custom time type that implements some SQL types:
- "database/sql".Scanner
- "database/sql/driver".Valuer

Running the tests

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.

Performance

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.

Contributors

matthias-margush - column aliasing via tags
Rob Figueiredo - @robfig
Quinn Slack - @sqs

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