Update func comments in chainable_api and FirstOr_ (#5935)

Add comments to functions in chainable_api. Depending on the method,
these comments add some additional context or details that are relevant
when reading the function, link to the actual docs at gorm.io/docs, or
provide examples of use. These comments should make GORM much more
pleasant to use with an IDE that provides hoverable comments, and are
minimal examples.

Also add in-code documentation to FirstOrInit and FirstOrCreate.

Almost all examples are directly pulled from the docs, with short
comments explaining the code. Most examples omit the `db.Model(&User{})`
for brevity, and would not actually work.

Co-authored-by: Nate Armstrong <nate.armstrong@eluv.io>

chainable_api.go

@@ -13,7 +13,7 @@ import (
 //
 //	// update all users's name to `hello`
 //	db.Model(&User{}).Update("name", "hello")
-//	// if user's primary key is non-blank, will use it as condition, then will only update the user's name to `hello`
+//	// if user's primary key is non-blank, will use it as condition, then will only update that user's name to `hello`
 //	db.Model(&user).Update("name", "hello")
 func (db *DB) Model(value interface{}) (tx *DB) {
 	tx = db.getInstance()
@@ -22,6 +22,19 @@ func (db *DB) Model(value interface{}) (tx *DB) {
 }
 
 // Clauses Add clauses
+//
+// This supports both standard clauses (clause.OrderBy, clause.Limit, clause.Where) and more
+// advanced techniques like specifying lock strength and optimizer hints. See the
+// [docs] for more depth.
+//
+//	// add a simple limit clause
+//	db.Clauses(clause.Limit{Limit: 1}).Find(&User{})
+//	// tell the optimizer to use the `idx_user_name` index
+//	db.Clauses(hints.UseIndex("idx_user_name")).Find(&User{})
+//	// specify the lock strength to UPDATE
+//	db.Clauses(clause.Locking{Strength: "UPDATE"}).Find(&users)
+//
+// [docs]: https://gorm.io/docs/sql_builder.html#Clauses
 func (db *DB) Clauses(conds ...clause.Expression) (tx *DB) {
 	tx = db.getInstance()
 	var whereConds []interface{}
@@ -45,6 +58,9 @@ func (db *DB) Clauses(conds ...clause.Expression) (tx *DB) {
 var tableRegexp = regexp.MustCompile(`(?i).+? AS (\w+)\s*(?:$|,)`)
 
 // Table specify the table you would like to run db operations
+//
+//	// Get a user
+//	db.Table("users").take(&result)
 func (db *DB) Table(name string, args ...interface{}) (tx *DB) {
 	tx = db.getInstance()
 	if strings.Contains(name, " ") || strings.Contains(name, "`") || len(args) > 0 {
@@ -66,6 +82,11 @@ func (db *DB) Table(name string, args ...interface{}) (tx *DB) {
 }
 
 // Distinct specify distinct fields that you want querying
+//
+//	// Select distinct names of users
+//	db.Distinct("name").Find(&results)
+//	// Select distinct name/age pairs from users
+//	db.Distinct("name", "age").Find(&results)
 func (db *DB) Distinct(args ...interface{}) (tx *DB) {
 	tx = db.getInstance()
 	tx.Statement.Distinct = true
@@ -76,6 +97,14 @@ func (db *DB) Distinct(args ...interface{}) (tx *DB) {
 }
 
 // Select specify fields that you want when querying, creating, updating
+//
+// Use Select when you only want a subset of the fields. By default, GORM will select all fields.
+// Select accepts both string arguments and arrays.
+//
+//	// Select name and age of user using multiple arguments
+//	db.Select("name", "age").Find(&users)
+//	// Select name and age of user using an array
+//	db.Select([]string{"name", "age"}).Find(&users)
 func (db *DB) Select(query interface{}, args ...interface{}) (tx *DB) {
 	tx = db.getInstance()
 
@@ -153,6 +182,17 @@ func (db *DB) Omit(columns ...string) (tx *DB) {
 }
 
 // Where add conditions
+//
+// See the [docs] for details on the various formats that where clauses can take. By default, where clauses chain with AND.
+//
+//	// Find the first user with name jinzhu
+//	db.Where("name = ?", "jinzhu").First(&user)
+//	// Find the first user with name jinzhu and age 20
+//	db.Where(&User{Name: "jinzhu", Age: 20}).First(&user)
+//	// Find the first user with name jinzhu and age not equal to 20
+//	db.Where("name = ?", "jinzhu").Where("age <> ?", "20").First(&user)
+//
+// [docs]: https://gorm.io/docs/query.html#Conditions
 func (db *DB) Where(query interface{}, args ...interface{}) (tx *DB) {
 	tx = db.getInstance()
 	if conds := tx.Statement.BuildCondition(query, args...); len(conds) > 0 {
@@ -162,6 +202,11 @@ func (db *DB) Where(query interface{}, args ...interface{}) (tx *DB) {
 }
 
 // Not add NOT conditions
+//
+// Not works similarly to where, and has the same syntax.
+//
+//	// Find the first user with name not equal to jinzhu
+//	db.Not("name = ?", "jinzhu").First(&user)
 func (db *DB) Not(query interface{}, args ...interface{}) (tx *DB) {
 	tx = db.getInstance()
 	if conds := tx.Statement.BuildCondition(query, args...); len(conds) > 0 {
@@ -171,6 +216,11 @@ func (db *DB) Not(query interface{}, args ...interface{}) (tx *DB) {
 }
 
 // Or add OR conditions
+//
+// Or is used to chain together queries with an OR.
+//
+//	// Find the first user with name equal to jinzhu or john
+//	db.Where("name = ?", "jinzhu").Or("name = ?", "john").First(&user)
 func (db *DB) Or(query interface{}, args ...interface{}) (tx *DB) {
 	tx = db.getInstance()
 	if conds := tx.Statement.BuildCondition(query, args...); len(conds) > 0 {
@@ -203,6 +253,9 @@ func (db *DB) Joins(query string, args ...interface{}) (tx *DB) {
 }
 
 // Group specify the group method on the find
+//
+//	// Select the sum age of users with given names
+//	db.Model(&User{}).Select("name, sum(age) as total").Group("name").Find(&results)
 func (db *DB) Group(name string) (tx *DB) {
 	tx = db.getInstance()
 
@@ -214,6 +267,9 @@ func (db *DB) Group(name string) (tx *DB) {
 }
 
 // Having specify HAVING conditions for GROUP BY
+//
+//	// Select the sum age of users with name jinzhu
+//	db.Model(&User{}).Select("name, sum(age) as total").Group("name").Having("name = ?", "jinzhu").Find(&result)
 func (db *DB) Having(query interface{}, args ...interface{}) (tx *DB) {
 	tx = db.getInstance()
 	tx.Statement.AddClause(clause.GroupBy{
@@ -222,7 +278,7 @@ func (db *DB) Having(query interface{}, args ...interface{}) (tx *DB) {
 	return
 }
 
-// Order specify order when retrieve records from database
+// Order specify order when retrieving records from database
 //
 //	db.Order("name DESC")
 //	db.Order(clause.OrderByColumn{Column: clause.Column{Name: "name"}, Desc: true})
@@ -247,13 +303,27 @@ func (db *DB) Order(value interface{}) (tx *DB) {
 }
 
 // Limit specify the number of records to be retrieved
+//
+// Limit conditions can be cancelled by using `Limit(-1)`.
+//
+//	// retrieve 3 users
+//	db.Limit(3).Find(&users)
+//	// retrieve 3 users into users1, and all users into users2
+//	db.Limit(3).Find(&users1).Limit(-1).Find(&users2)
 func (db *DB) Limit(limit int) (tx *DB) {
 	tx = db.getInstance()
 	tx.Statement.AddClause(clause.Limit{Limit: &limit})
 	return
 }
 
 // Offset specify the number of records to skip before starting to return the records
+//
+// Offset conditions can be cancelled by using `Offset(-1)`.
+//
+//	// select the third user
+//	db.Offset(2).First(&user)
+//	// select the first user by cancelling an earlier chained offset
+//	db.Offset(5).Offset(-1).First(&user)
 func (db *DB) Offset(offset int) (tx *DB) {
 	tx = db.getInstance()
 	tx.Statement.AddClause(clause.Limit{Offset: offset})
@@ -281,6 +351,7 @@ func (db *DB) Scopes(funcs ...func(*DB) *DB) (tx *DB) {
 
 // Preload preload associations with given conditions
 //
+//	// get all users, and preload all non-cancelled orders
 //	db.Preload("Orders", "state NOT IN (?)", "cancelled").Find(&users)
 func (db *DB) Preload(query string, args ...interface{}) (tx *DB) {
 	tx = db.getInstance()
@@ -291,12 +362,41 @@ func (db *DB) Preload(query string, args ...interface{}) (tx *DB) {
 	return
 }
 
+// Attrs provide attributes used in [FirstOrCreate] or [FirstOrInit]
+//
+// Attrs only adds attributes if the record is not found.
+//
+//	// assign an email if the record is not found
+//	db.Where(User{Name: "non_existing"}).Attrs(User{Email: "fake@fake.org"}).FirstOrInit(&user)
+//	// user -> User{Name: "non_existing", Email: "fake@fake.org"}
+//
+//	// assign an email if the record is not found, otherwise ignore provided email
+//	db.Where(User{Name: "jinzhu"}).Attrs(User{Email: "fake@fake.org"}).FirstOrInit(&user)
+//	// user -> User{Name: "jinzhu", Age: 20}
+//
+// [FirstOrCreate]: https://gorm.io/docs/advanced_query.html#FirstOrCreate
+// [FirstOrInit]: https://gorm.io/docs/advanced_query.html#FirstOrInit
 func (db *DB) Attrs(attrs ...interface{}) (tx *DB) {
 	tx = db.getInstance()
 	tx.Statement.attrs = attrs
 	return
 }
 
+// Assign provide attributes used in [FirstOrCreate] or [FirstOrInit]
+//
+// Assign adds attributes even if the record is found. If using FirstOrCreate, this means that
+// records will be updated even if they are found.
+//
+//	// assign an email regardless of if the record is not found
+//	db.Where(User{Name: "non_existing"}).Assign(User{Email: "fake@fake.org"}).FirstOrInit(&user)
+//	// user -> User{Name: "non_existing", Email: "fake@fake.org"}
+//
+//	// assign email regardless of if record is found
+//	db.Where(User{Name: "jinzhu"}).Assign(User{Email: "fake@fake.org"}).FirstOrInit(&user)
+//	// user -> User{Name: "jinzhu", Age: 20, Email: "fake@fake.org"}
+//
+// [FirstOrCreate]: https://gorm.io/docs/advanced_query.html#FirstOrCreate
+// [FirstOrInit]: https://gorm.io/docs/advanced_query.html#FirstOrInit
 func (db *DB) Assign(attrs ...interface{}) (tx *DB) {
 	tx = db.getInstance()
 	tx.Statement.assigns = attrs

finisher_api.go

@@ -294,6 +294,16 @@ func (db *DB) assignInterfacesToValue(values ...interface{}) {
 
 // FirstOrInit finds the first matching record, otherwise if not found initializes a new instance with given conds.
 // Each conds must be a struct or map.
+//
+// FirstOrInit never modifies the database. It is often used with Assign and Attrs.
+//
+//	// assign an email if the record is not found
+//	db.Where(User{Name: "non_existing"}).Attrs(User{Email: "fake@fake.org"}).FirstOrInit(&user)
+//	// user -> User{Name: "non_existing", Email: "fake@fake.org"}
+//
+//	// assign email regardless of if record is found
+//	db.Where(User{Name: "jinzhu"}).Assign(User{Email: "fake@fake.org"}).FirstOrInit(&user)
+//	// user -> User{Name: "jinzhu", Age: 20, Email: "fake@fake.org"}
 func (db *DB) FirstOrInit(dest interface{}, conds ...interface{}) (tx *DB) {
 	queryTx := db.Limit(1).Order(clause.OrderByColumn{
 		Column: clause.Column{Table: clause.CurrentTable, Name: clause.PrimaryKey},
@@ -321,6 +331,18 @@ func (db *DB) FirstOrInit(dest interface{}, conds ...interface{}) (tx *DB) {
 
 // FirstOrCreate finds the first matching record, otherwise if not found creates a new instance with given conds.
 // Each conds must be a struct or map.
+//
+// Using FirstOrCreate in conjunction with Assign will result in an update to the database even if the record exists.
+//
+//	// assign an email if the record is not found
+//	result := db.Where(User{Name: "non_existing"}).Attrs(User{Email: "fake@fake.org"}).FirstOrCreate(&user)
+//	// user -> User{Name: "non_existing", Email: "fake@fake.org"}
+//	// result.RowsAffected -> 1
+//
+//	// assign email regardless of if record is found
+//	result := db.Where(User{Name: "jinzhu"}).Assign(User{Email: "fake@fake.org"}).FirstOrCreate(&user)
+//	// user -> User{Name: "jinzhu", Age: 20, Email: "fake@fake.org"}
+//	// result.RowsAffected -> 1
 func (db *DB) FirstOrCreate(dest interface{}, conds ...interface{}) (tx *DB) {
 	tx = db.getInstance()
 	queryTx := db.Session(&Session{}).Limit(1).Order(clause.OrderByColumn{