How to close PreparedStatement in golang

PreparedStatement objects are often used in database-related operations in Golang. PreparedStatement is designed to optimize SQL statements sent from the application to the database. Unlike Statements, prepared statements are compiled for a specific type when they are created, rather than compiled each time they are executed. This compilation process can improve query execution efficiency, and is also more secure and can avoid SQL injection attacks. But closing PreparedStatement in a timely manner when it is no longer needed is an important part of memory management. This article will discuss how to close PreparedStatement.

1. Creation of prepared statements

Creating PreparedStatament is usually done through the db.Prepare method. The specific usage is as follows:

stmt, err := db.Prepare("select * from users where username = ?;")

In this example, we use prepared statements to query all users in the database whose username is equal to "?".

2. Execution of prepared statements

After creating the prepared statement, we need to execute the prepared statement. The specific usage is as follows:

res, err := stmt.Exec("Jack")

In this example, we use the previously created prepared statement stmt, pass the parameter "Jack" in, and execute it through the stmt.Exec method. When the prepared statement is executed, all "?" will be replaced with actual parameter values ​​and then sent to the database for query. The results of the query are returned in Result type data. At this point, we have completed the use of prepared statements.

3. Closing PreparedStatement

When PreparedStatement is no longer needed, we need to close it to release resources. There are two ways to close PreparedStatement. Method one is to directly call stmt.Close() to close it. The code is as follows:

stmt.Close()

Method two is to set stmt to nil, which is a more security-oriented approach. , because in Go language, it is unsafe to forcefully close an already closed object. The specific usage is as follows:

stmt = nil

It is worth noting that when we close PreparedStatement, the Result associated with it will not be automatically closed. Therefore, when we close PreparedStatement, we must close Result to avoid memory leaks.

res.Close()

4. Handling of memory leaks

When using prepared statements, you need to pay attention. If PreparedStatement and Result are not closed manually, memory leaks may occur.

In actual development, prepared statements are usually created in functions, and variables are automatically released when the scope exits. If the developer does not manually close PreparedStatement and Result, the memory occupied by them will not be released when the function exits, which will cause a memory leak. Therefore, in order to avoid memory leaks, we need to manually close PreparedStatement and Result before the function exits.

func GetUser(username string) ([]User, error) {
    stmt, err := db.Prepare("select * from users where username = ?;")
    if err != nil {
        return nil, err
    }
    defer stmt.Close()

    res, err := stmt.Exec(username)
    if err != nil {
        return nil, err
    }
    defer res.Close()

    // 从res中获取数据并处理

    return users, nil
}

In this example, we manually closed PreparedStatement and Result to ensure that the memory occupied by these objects is released correctly when the function exits. This example can be applied to other database operations.

In short, for prepared statements, you must remember to close PreparedStatement and Result after use, otherwise memory leaks will occur. There are two ways to close PreparedStatement, namely calling stmt.Close() or setting stmt to nil. It is recommended to use the second method.

The above is the detailed content of How to close PreparedStatement in golang. For more information, please follow other related articles on the PHP Chinese website!