db.Mux.Unlock()
		// wait for other goroutines prepared
		<-stmt.prepared
		if stmt.prepareErr != nil {
			return Stmt{}, stmt.prepareErr
		}

		return *stmt, nil
	}

	// cache preparing stmt first
	cacheStmt := Stmt{Transaction: isTransaction, prepared: make(chan struct{})}
	db.Stmts[query] = &cacheStmt
	db.Mux.Unlock()

	// prepare completed
	defer close(cacheStmt.prepared)

	}
	AssertAssociationCount(t, user2, "Account", 0, "after delete")

	// Prepare Data for Clear
	account = Account{Number: "account-has-one-append"}
	if err := DB.Model(&user2).Association("Account").Append(&account); err != nil {
		t.Fatalf("Error happened when append Account, got %v", err)
	}

	AssertAssociationCount(t, user2, "Account", 1, "after prepare data")

	// Clear

		// enable prepare statement
		tx3 := DB.Session(&gorm.Session{PrepareStmt: true})
		if err := tx3.Transaction(func(tx4 *gorm.DB) error {
			// nested transaction
			return tx4.Transaction(func(tx5 *gorm.DB) error {
				return tx5.First(&User{}, "name = ?", "transaction-2").Error
			})
		}); err != nil {
			t.Fatalf("prepare statement and nested transcation coexist" + err.Error())
		}
	})

		t.Fatalf("Error happened when append Manager, got %v", err)
	}

	AssertAssociationCount(t, user2, "Company", 1, "after prepare data")
	AssertAssociationCount(t, user2, "Manager", 1, "after prepare data")

	// Clear
	if err := DB.Model(&user2).Association("Company").Clear(); err != nil {
		t.Errorf("Error happened when clear Company, got %v", err)
	}

	}
	AssertAssociationCount(t, user2, "Languages", 0, "after delete")

	// Prepare Data for Clear
	if err := DB.Model(&user2).Association("Languages").Append(&language); err != nil {
		t.Fatalf("Error happened when append Languages, got %v", err)
	}

	AssertAssociationCount(t, user2, "Languages", 1, "after prepare data")

	// Clear
	if err := DB.Model(&user2).Association("Languages").Clear(); err != nil {

* 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
* SQL Builder, Upsert, Locking, Optimizer/Index/Comment Hints, NamedArg, Search/Update/Create with SQL Expr
* Composite Primary Key
* Auto Migrations

		// close prepared statement, because SavePoint not support prepared statement.
		// e.g. mysql8.0 doc: https://dev.mysql.com/doc/refman/8.0/en/sql-prepared-statements.html
		var (
			preparedStmtTx   *PreparedStmtTX
			isPreparedStmtTx bool
		)
		// close prepared statement, because SavePoint not support prepared statement.

	}
	AssertAssociationCount(t, user2, "Pets", 0, "after delete")

	// Prepare Data for Clear
	if err := DB.Model(&user2).Association("Pets").Append(&pet); err != nil {
		t.Fatalf("Error happened when append Pets, got %v", err)
	}

	AssertAssociationCount(t, user2, "Pets", 1, "after prepare data")

	// Clear
	if err := DB.Model(&user2).Association("Pets").Clear(); err != nil {

# Test Guide

```bash
cd tests
# prepare test databases
docker-compose up

# run all tests
./tests_all.sh

package gorm

import (
	"database/sql"
	"database/sql/driver"
	"reflect"
	"time"

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

// prepareValues prepare values slice
func prepareValues(values []interface{}, db *DB, columnTypes []*sql.ColumnType, columns []string) {
	if db.Statement.Schema != nil {
		for idx, name := range columns {
			if field := db.Statement.Schema.LookUpField(name); field != nil {