The upper.io/db.v1/postgresql adapter for PostgreSQL is based on the
github.com/lib/pq driver by Blake Mizerany.
This adapter supports basic CRUD queries, transactions, simple join queries and raw SQL.
Use go get to download and install the adapter:
go get upper.io/db.v1/postgresql
The postgresql.ConnectionURL{} struct is defined like this:
// ConnectionURL implements a PostgreSQL connection struct.
type ConnectionURL struct {
User string
Password string
Address db.Address
Database string
Options map[string]string
}
The db.Address interface can be satisfied by the db.Host(),
db.HostPort() or db.Socket() functions.
Alternatively, a postgresql.ParseURL() function is provided:
// ParseURL parses s into a ConnectionURL struct.
postgresql.ParseURL(s string) (ConnectionURL, error)
You may use a postgresql.ConnectionURL value as argument for db.Open().
To use this adapter, import upper.io/db.v1 and the upper.io/db.v1/postgresql
packages.
# main.go
package main
import (
"upper.io/db.v1"
"upper.io/db.v1/postgresql"
)
Then, you can use the db.Open() method to connect to a PostgreSQL server:
var settings = postgresql.ConnectionURL{
Address: db.Host("localhost"), // PostgreSQL server IP or name.
Database: "peanuts", // Database name.
User: "cbrown", // Optional user name.
Password: "snoopy", // Optional user password.
}
sess, err = db.Open(postgresql.Adapter, settings)
The following SQL statement creates a table with “name” and “born” columns.
--' example.sql
DROP TABLE IF EXISTS "birthday";
CREATE TABLE "birthday" (
"name" CHARACTER VARYING(50),
"born" TIMESTAMP
);
Use the psql command line tool to create the birthday table on the
upperio_tests database.
cat example.sql | PGPASSWORD=upperio psql -Uupperio upperio_tests
The Go code below will add some rows to the “birthday” table and then will print the same rows that were inserted.
// example.go
package main
import (
"fmt"
"log"
"time"
"upper.io/db.v1" // Imports the main db package.
_ "upper.io/db.v1/postgresql" // Imports the postgresql adapter.
)
var settings = postgresql.ConnectionURL{
Database: `upperio_tests`, // Database name.
Address: postgresql.Socket(`/var/run/postgresql/`), // Using unix sockets.
User: `upperio`, // Database username.
Password: `upperio`, // Database password.
}
type Birthday struct {
// Maps the "Name" property to the "name" column of the "birthday" table.
Name string `db:"name"`
// Maps the "Born" property to the "born" column of the "birthday" table.
Born time.Time `db:"born"`
}
func main() {
// Attemping to establish a connection to the database.
sess, err := db.Open(postgresql.Adapter, settings)
if err != nil {
log.Fatalf("db.Open(): %q\n", err)
}
// Remember to close the database session.
defer sess.Close()
// Pointing to the "birthday" table.
birthdayCollection, err := sess.Collection("birthday")
if err != nil {
log.Fatalf("sess.Collection(): %q\n", err)
}
// Attempt to remove existing rows (if any).
err = birthdayCollection.Truncate()
if err != nil {
log.Fatalf("Truncate(): %q\n", err)
}
// Inserting some rows into the "birthday" table.
birthdayCollection.Append(Birthday{
Name: "Hayao Miyazaki",
Born: time.Date(1941, time.January, 5, 0, 0, 0, 0, time.UTC),
})
birthdayCollection.Append(Birthday{
Name: "Nobuo Uematsu",
Born: time.Date(1959, time.March, 21, 0, 0, 0, 0, time.UTC),
})
birthdayCollection.Append(Birthday{
Name: "Hironobu Sakaguchi",
Born: time.Date(1962, time.November, 25, 0, 0, 0, 0, time.UTC),
})
// Let's query for the results we've just inserted.
var res db.Result
res = birthdayCollection.Find()
var birthday []Birthday
// Query all results and fill the birthday variable with them.
err = res.All(&birthday)
if err != nil {
log.Fatalf("res.All(): %q\n", err)
}
// Printing to stdout.
for _, birthday := range birthday {
fmt.Printf("%s was born in %s.\n", birthday.Name, birthday.Born.Format("January 2, 2006"))
}
}
Running the example above:
go run main.go
Expected output:
Hayao Miyazaki was born in January 5, 1941.
Nobuo Uematsu was born in March 21, 1959.
Hironobu Sakaguchi was born in November 25, 1962.
Querying from multiple tables is possible using db.Database.Collection(),
just pass the name of all the tables separating them by commas. You can also
use the AS keyword to define an alias that you could later use in conditions
to refer to the original table.
var err error
var artistPublication db.Collection
// Querying from two tables.
artistPublication, err = sess.Collection(`artist AS a`, `publication AS p`)
if err != nil {
log.Fatal(err)
}
res := artistPublication.Find(
// Use db.Raw{} to enclose statements that you'd like to pass without
// filtering.
db.Raw{`a.id = p.author_id`},
).Select(
`p.id`, // We defined "p" as an alias for "publication".
`p.title as publication_title`, // The "AS" is recognized as column alias.
db.Raw{`a.name AS artist_name`},
)
type artistPublication_t struct {
ID int64 `db:"id"`
PublicationTitle string `db:"publication_title"`
ArtistName string `db:"artist_name"`
}
all := []artistPublication_t{}
if err = res.All(&all); err != nil {
log.Fatal(err)
}
If you’re working with more than one collection, the first one you pass becomes
your primary collection. Calls to db.Collection.Append(),
db.Collection.Remove() and db.Collection.Update() will be performed on your
primary collection.
If you want to use auto-increment (or serial) keys with PostgreSQL database,
you must define the column type as SERIAL, like this:
CREATE TABLE foo(
id SERIAL PRIMARY KEY,
title VARCHAR
);
Also, you must provide the omitempty option in the db tag when defining the
struct:
type Foo struct {
ID int64 `db:"id,omitempty"`
Title string `db:"title"`
}
Otherwise, you’ll end up with an error like this:
ERROR: duplicate key violates unique constraint "id"
In order for the ID to be returned by db.Collection.Append(), the SERIAL field
must be set as PRIMARY KEY.
Sometimes you’ll need to run complex SQL queries with joins and database
specific magic, there is an extra package sqlutil that you could use in this
situation:
import "upper.io/db.v1/util/sqlutil"
This is an example for sqlutil.FetchRows:
var sess db.Database
var rows *sql.Rows
var err error
var drv *sql.DB
type publication_t struct {
ID int64 `db:"id,omitempty"`
Title string `db:"title"`
AuthorID int64 `db:"author_id"`
}
if sess, err = db.Open(Adapter, settings); err != nil {
t.Fatal(err)
}
defer sess.Close()
drv = sess.Driver().(*sql.DB)
rows, err = drv.Query(`
SELECT
p.id,
p.title AS publication_title,
a.name AS artist_name
FROM
artist AS a,
publication AS p
WHERE
a.id = p.author_id
`)
if err != nil {
t.Fatal(err)
}
var all []publication_t
// Mapping to an array.
if err = sqlutil.FetchRows(rows, &all); err != nil {
t.Fatal(err)
}
if len(all) != 9 {
t.Fatalf("Expecting some rows.")
}
You can also use sqlutil.FetchRow(*sql.Rows, interface{}) for mapping results
obtained from sql.DB.Query() calls to a pointer of a single struct instead of
a pointer to an array of structs. Please note that there is no support for
sql.DB.QueryRow() and that you must provide a *sql.Rows value to both
sqlutil.FetchRow() and sqlutil.FetchRows().
db.Raw and db.FuncIf you need to provide a raw parameter for a method you can use the db.Raw
type. Plese note that raw means that the specified value won’t be filtered:
res = sess.Find().Select(db.Raw{`DISTINCT(name)`})
db.Raw also works for condition values.
Another useful type that you could use to create an equivalent statement is
db.Func:
res = sess.Find().Select(db.Func{`DISTINCT`, `name`})