Database Indexes

GORM allows create database index with tag index, uniqueIndex, those indexes will be created when AutoMigrate or CreateTable with GORM

Index Tag

GORM accepts lots of index settings, like class, type, where, comment, expression, sort, collate

Check the following example for how to use it

type User struct {
  Name  string `gorm:"index"`
  Name2 string `gorm:"index:idx_name,unique"`
  Name3 string `gorm:"index:,sort:desc,collate:utf8,type:btree,length:10,where:name3 != 'jinzhu'"`
  Name4 string `gorm:"uniqueIndex"`
  Age   int64  `gorm:"index:,class:FULLTEXT,comment:hello \\, world,where:age > 10"`
  Age2  int64  `gorm:"index:,expression:ABS(age)"`
}

uniqueIndex

tag uniqueIndex works similar like index, it equals to index:,unique

type User struct {
  Name1 string `gorm:"uniqueIndex"`
  Name2 string `gorm:"uniqueIndex:idx_name,sort:desc"`
}

Composite Indexes

Use same index name for two fields will creates composite indexes, for example:

type User struct {
  Name   string `gorm:"index:idx_member"`
  Number string `gorm:"index:idx_member"`
}

Fields Priority

The column order of a composite index has an impact on its performance so it must be chosen carefully

You can specify the order with the priority option, the default priority value is 10, if priority value is the same, the order will be based on model struct’s field index

type User struct {
  Name   string `gorm:"index:idx_member"`
  Number string `gorm:"index:idx_member"`
}
// column order: name, number

type User struct {
  Name   string `gorm:"index:idx_member,priority:2"`
  Number string `gorm:"index:idx_member,priority:1"`
}
// column order: number, name

type User struct {
  Name   string `gorm:"index:idx_member,priority:12"`
  Number string `gorm:"index:idx_member"`
}
// column order: number, name

Multiple indexes

A field accepts multiple index, uniqueIndex tags that will create multiple indexes on a field

type UserIndex struct {
  OID          int64  `gorm:"index:idx_id;index:idx_oid,unique"`
  MemberNumber string `gorm:"index:idx_id"`
}