relation, ok := db.Statement.Schema.Relationships.Relations[join.Name]
					if ok {
						isRelations = true
						relations = append(relations, relation)
					} else {
						// handle nested join like "Manager.Company"
						nestedJoinNames := strings.Split(join.Name, ".")
						if len(nestedJoinNames) > 1 {
							isNestedJoin := true

	// DisableForeignKeyConstraintWhenMigrating
	DisableForeignKeyConstraintWhenMigrating bool
	// IgnoreRelationshipsWhenMigrating
	IgnoreRelationshipsWhenMigrating bool
	// DisableNestedTransaction disable nested transaction
	DisableNestedTransaction bool
	// AllowGlobalUpdate allow global update
	AllowGlobalUpdate bool
	// QueryFields executes the SQL query with all fields of the table
	QueryFields bool

// they are rolled back.
func (db *DB) Transaction(fc func(tx *DB) error, opts ...*sql.TxOptions) (err error) {
	panicked := true

	if committer, ok := db.Statement.ConnPool.(TxCommitter); ok && committer != nil {
		// nested transaction
		if !db.DisableNestedTransaction {
			err = db.SavePoint(fmt.Sprintf("sp%p", fc)).Error
			if err != nil {
				return
			}
			defer func() {

* Full-Featured ORM
* Associations (Has One, Has Many, Belongs To, Many To Many, Polymorphism, Single-table inheritance)
* Hooks (Before/After Create/Save/Update/Delete/Find)
* Eager loading with `Preload`, `Joins`
* Transactions, Nested Transactions, Save Point, RollbackTo to Saved Point
* Context, Prepared Statement Mode, DryRun Mode
* Batch Insert, FindInBatches, Find To Map

	}

	var find1 Value
	err := DB.Joins("Nested").Joins("Nested.Join").Preload("Nested.Preloads").First(&find1, value1.ID).Error
	if err != nil {
		t.Errorf("failed to find value, got err: %v", err)
	}
	AssertEqual(t, find1, value1)

	var find2 Value
	// Joins will automatically add Nested queries.
	err = DB.Joins("Nested.Join").Preload("Nested.Preloads").First(&find2, value2.ID).Error
	if err != nil {

	users := []User{
		{
			Name: "nested-joins-1",
			Manager: &User{
				Name: "nested-joins-manager-1",
				Company: Company{
					Name: "nested-joins-manager-company-1",
				},
				NamedPet: &Pet{
					Name: "nested-joins-manager-namepet-1",
					Toy: Toy{
						Name: "nested-joins-manager-namepet-toy-1",
					},
				},
			},

		return strconv.FormatUint(v, 10)
	}
	return ""
}

const nestedRelationSplit = "__"

// NestedRelationName nested relationships like `Manager__Company`
func NestedRelationName(prefix, name string) string {
	return prefix + nestedRelationSplit + name
}

// SplitNestedRelationName Split nested relationships to `[]string{"Manager","Company"}`
func SplitNestedRelationName(name string) []string {

							}
						} else {
							matchedFieldCount[column] = 1
						}
					} else if names := utils.SplitNestedRelationName(column); len(names) > 1 { // has nested relation
						if rel, ok := sch.Relationships.Relations[names[0]]; ok {
							subNameCount := len(names)
							// nested relation fields
							relFields := make([]*schema.Field, 0, subNameCount-1)
							relFields = append(relFields, rel.Field)

package callbacks

import (
	"fmt"
	"reflect"
	"sort"
	"strings"

	"gorm.io/gorm"
	"gorm.io/gorm/clause"
	"gorm.io/gorm/schema"
	"gorm.io/gorm/utils"
)

// parsePreloadMap extracts nested preloads. e.g.
//
//	// schema has a "k0" relation and a "k7.k8" embedded relation
//	parsePreloadMap(schema, map[string][]interface{}{
//		clause.Associations: {"arg1"},
//		"k1":                {"arg2"},

	// Composite Index: Flattened structure.
	Data0A string `gorm:"index:,composite:comp_id0"`
	Data0B string `gorm:"index:,composite:comp_id0"`

	// Composite Index: Nested structure.
	Data1A string `gorm:"index:,composite:comp_id1"`
	CompIdxLevel1C

	// Composite Index: Unique and priority.
	Data2A string `gorm:"index:,unique,composite:comp_id2,priority:2"`
	CompIdxLevel2C
}