Go Relational Persistence

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

# install the library:
go get github.com/coopernurse/gorp

// use in your .go code:
import (
    "github.com/coopernurse/gorp"
)

API Documentation

Full godoc output from the latest code in master is available here:

http://godoc.org/github.com/coopernurse/gorp

Quickstart

package main

import (
    "database/sql"
    "github.com/coopernurse/gorp"
    _ "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)
    }
}

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)
//
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")

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 goose: https://bitbucket.org/liamstask/goose).

// 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"}
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!")
}

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
    }

    trans.Insert(per)
    inv.PersonId = per.Id
    trans.Insert(inv)

    // 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

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)
}

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.

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})

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: ziutek/mymysql#77

To avoid any potential issues with timezone/DST, consider using an integer field for time data and storing UNIX time.

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", "postgres", "sqlite3" 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.

Pull requests / Contributions

Contributions are very welcome. Please follow these guidelines:

• Fork the develop branch and issue pull requests targeting the develop branch
  • If you don't do this, I'll likely cherry pick your commit into develop
• If you are adding an enhancement, please open an issue first with your proposed change.
• Changes that break backwards compatibility in the public API are only accepted after we discuss on a GitHub issue for a while.

Thanks!

Contributors

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