package main
import (
"database/sql"
"errors"
"fmt"
_ "github.com/bmizerany/pq"
"os"
"regexp"
"strings"
)
func main() {
db := dbConnect()
makeTestTables(db)
defer db.Close()
defer cleanup(db)
// Insert Some Data
db.Exec(`INSERT INTO array_test VALUES ('{"String1", "String2"}')`)
// arrays can be selected as strings...
dataString := selectAsString(db)
fmt.Println("SELECT as String:", dataString)
// Or by using array functions...
dataUnnest := selectUsingUnnest(db)
fmt.Println("SELECT using Unnest:", dataUnnest)
// Or by defining a scan type and parsing the return value
dataSlice := selectAsSlice(db)
fmt.Println("SELECT by parsing:", dataSlice)
// Arrays can be updated by replacing the entire array:
newArray := []interface{}{"String1", "String3", "String4", "String5"}
updateArray(db, newArray)
dataSlice = selectAsSlice(db)
fmt.Println("UPDATE entire array", dataSlice)
// or by appending / prepending value(s):
AppendToArray(db, "String6")
dataSlice = selectAsSlice(db)
fmt.Println("UPDATE with append:", dataSlice)
// or by replacing individual values:
ReplaceInArray(db, 2, "NULL")
dataSlice = selectAsSlice(db)
fmt.Println("UPDATE with replace:", dataSlice)
// Deleting by index requires slicing and is inefficient:
DeleteFromArray(db, 3)
dataSlice = selectAsSlice(db)
fmt.Println("UPDATE deleting index:", dataSlice)
}
// Arrays are serialized to strings {value, value...} by the database.
// these strings selected, updated and inserted like any string
func selectAsString(db *sql.DB) string {
row := db.QueryRow("SELECT data FROM array_test")
var asString string
err := row.Scan(&asString)
if err != nil {
panic(err)
}
return asString
}
// The UNNEST function expands an array into multiple rows. Each row
// can then be scanned individually.
func selectUsingUnnest(db *sql.DB) []string {
results := make([]string, 0)
rows, err := db.Query("SELECT UNNEST(data) FROM array_test")
if err != nil {
panic(err)
}
var scanString string
for rows.Next() {
rows.Scan(&scanString)
results = append(results, scanString)
}
return results
}
// By defining a wrapper type around a slice which implements
// sql.Scanner, we can scan the array directly into the type.
func selectAsSlice(db *sql.DB) StringSlice {
row := db.QueryRow("SELECT data FROM array_test")
var asSlice StringSlice
err := row.Scan(&asSlice)
if err != nil {
panic(err)
}
return asSlice
}
// Update an array by replacing the whole array with new values.
// This _could_ be done by serializing the StringSlice type using
// sql.driver.Valuer, but then we would have to validate the type
// of each value manually and format it for insert by hand. Instead,
// the ARRAY[...] format allows us to use query parameters to construct
// the array, ie ARRAY[$1, $2, $3], which then allows the database
// driver to coerce the variables into the right format for us.
func updateArray(db *sql.DB, array []interface{}) {
params := make([]string, 0, len(array))
for i := range array {
params = append(params, fmt.Sprintf("$%v", i+1))
}
query := fmt.Sprintf("UPDATE array_test SET data = ARRAY[%s]", strings.Join(params, ", "))
db.Exec(query, array...)
}
// The ARRAY_APPEND and ARRAY_PREPEND functions can be used to add single
// values to arrays. ARRAY_CAT combines two arrays. The || operator can
// do the same thing:
// SET data = data || <value>
// SET data = data || ARRAY[<value1>, <value2>]
func AppendToArray(db *sql.DB, value string) {
_, err := db.Exec("UPDATE array_test SET data = ARRAY_APPEND(data, $1)", value)
if err != nil {
panic(err)
}
}
// Arrays are 1-indexed. Individual elements can be used in expressions,
// updated, or selected by indexing the array.
func ReplaceInArray(db *sql.DB, index int, newValue string) {
_, err := db.Exec("UPDATE array_test SET data[$1] = $2", index, newValue)
if err != nil {
panic(err)
}
}
// Arrays support slice indexing:
// ARRAY['a', 'b', 'c'][1:2] == ARRAY['a', 'b']
// The ARRAY_UPPER function gets the length of an array for a specified dimension
// Deleting a value from an array amounts to slicing the array into two parts
// and combining them back together.
func DeleteFromArray(db *sql.DB, i int) {
_, err := db.Exec("UPDATE array_test SET data = array_cat(data[0:$1], data[$2:ARRAY_UPPER(data, 1) + 1])", i-1, i+1)
if err != nil {
panic(err)
}
}
type StringSlice []string
// Implements sql.Scanner for the String slice type
// Scanners take the database value (in this case as a byte slice)
// and sets the value of the type. Here we cast to a string and
// do a regexp based parse
func (s *StringSlice) Scan(src interface{}) error {
asBytes, ok := src.([]byte)
if !ok {
return error(errors.New("Scan source was not []bytes"))
}
asString := string(asBytes)
parsed := parseArray(asString)
(*s) = StringSlice(parsed)
return nil
}
// PARSING ARRAYS
// SEE http://www.postgresql.org/docs/9.1/static/arrays.html#ARRAYS-IO
// Arrays are output within {} and a delimiter, which is a comma for most
// postgres types (; for box)
//
// Individual values are surrounded by quotes:
// The array output routine will put double quotes around element values if
// they are empty strings, contain curly braces, delimiter characters,
// double quotes, backslashes, or white space, or match the word NULL.
// Double quotes and backslashes embedded in element values will be
// backslash-escaped. For numeric data types it is safe to assume that double
// quotes will never appear, but for textual data types one should be prepared
// to cope with either the presence or absence of quotes.
// construct a regexp to extract values:
var (
// unquoted array values must not contain: (" , \ { } whitespace NULL)
// and must be at least one char
unquotedChar = `[^",\\{}\s(NULL)]`
unquotedValue = fmt.Sprintf("(%s)+", unquotedChar)
// quoted array values are surrounded by double quotes, can be any
// character except " or \, which must be backslash escaped:
quotedChar = `[^"\\]|\\"|\\\\`
quotedValue = fmt.Sprintf("\"(%s)*\"", quotedChar)
// an array value may be either quoted or unquoted:
arrayValue = fmt.Sprintf("(?P<value>(%s|%s))", unquotedValue, quotedValue)
// Array values are separated with a comma IF there is more than one value:
arrayExp = regexp.MustCompile(fmt.Sprintf("((%s)(,)?)", arrayValue))
valueIndex int
)
// Find the index of the 'value' named expression
func init() {
for i, subexp := range arrayExp.SubexpNames() {
if subexp == "value" {
valueIndex = i
break
}
}
}
// Parse the output string from the array type.
// Regex used: (((?P<value>(([^",\\{}\s(NULL)])+|"([^"\\]|\\"|\\\\)*")))(,)?)
func parseArray(array string) []string {
results := make([]string, 0)
matches := arrayExp.FindAllStringSubmatch(array, -1)
for _, match := range matches {
s := match[valueIndex]
// the string _might_ be wrapped in quotes, so trim them:
s = strings.Trim(s, "\"")
results = append(results, s)
}
return results
}
// DB HELPERs
func dbConnect() *sql.DB {
datname := os.Getenv("PGDATABASE")
sslmode := os.Getenv("PGSSLMODE")
if datname == "" {
os.Setenv("PGDATABASE", "pqgotest")
}
if sslmode == "" {
os.Setenv("PGSSLMODE", "disable")
}
conn, err := sql.Open("postgres", "")
if err != nil {
panic(err)
}
return conn
}
// Create a table with an array type
// Can also use the syntax CREATE TABLE array_test (data varchar ARRAY)
func makeTestTables(db *sql.DB) {
_, err := db.Exec("CREATE TABLE array_test (data varchar[])")
if err != nil {
panic(err)
}
}
func cleanup(db *sql.DB) {
db.Exec("DROP TABLE array_test")
}