Using Database Transactions

12002

1. Background

In a database, a transaction refers to a series of database operations that are treated as a single execution unit. The goal of a transaction is to ensure the consistency and integrity of the database, allowing it to recover to its previous state even in the event of errors or interruptions. Transactions are typically used in scenarios where the atomicity of multiple database operations needs to be guaranteed.

When to Use Transactions

Multi-step business operations:
When a business operation requires multiple steps to be executed, either all must succeed or all must fail, transactions can be used. For example, a bank transfer operation involves deducting an amount from one account and adding it to another; both steps must either succeed or fail together.
Ensuring data integrity:
When there are dependencies between multiple data operations that need to ensure data integrity, transactions can be used. For instance, in an order system, updating both order information and inventory information simultaneously requires that both operations either succeed or fail together.
Preventing concurrency issues:
In situations where multiple users access the database concurrently, data races and consistency issues may arise. Transactions can provide a locking mechanism to ensure that other transactions cannot modify the same data during the execution of one transaction.

2. Characteristics

Characteristics of Transactions
1. Atomicity: A transaction is an atomic operation; it either fully succeeds or fully rolls back.
2. Consistency: The execution of a transaction moves the database from one consistent state to another.
3. Isolation: The execution of concurrent transactions does not interfere with each other; the data seen by each transaction during execution is independent.
4. Durability: Once a transaction is committed, its changes will be permanently saved in the database.
Problems Solved by Transactions
1. Data consistency issues: Transactions ensure the atomicity of multiple operations, preventing data inconsistency issues that may arise from partial successes or failures.
2. Concurrency issues: Through the isolation of transactions, data races and consistency issues caused by concurrent execution of multiple transactions are prevented.

3. Example

Two student records will be inserted into a database table named student. If both insert operations are successfully executed, if either of the insert operations fails, the entire transaction will be rolled back, ensuring the consistency of the database. This approach guarantees that both insert operations either succeed simultaneously or fail simultaneously, thereby maintaining the integrity of the database.

await jianghuKnex.transaction(async trx => {  
    await trx('student').insert({ name: 'xxx1' });  
    await trx('student').insert({ name: 'xxx2' });  
});

How to Use Database Transactions

In most relational databases, the use of transactions typically involves the following steps:
1. Start the transaction: Initiate a new transaction by executing BEGIN TRANSACTION or a similar statement.
2. Execute transaction operations: Perform a series of database operations within the transaction, including data insertion, deletion, modification, and querying.
3. Commit the transaction: Execute the COMMIT statement to permanently save the changes of the transaction to the database.
4. Roll back the transaction: If an error or other unpredictable situation occurs during the execution of the transaction, the ROLLBACK statement can be executed to undo all modifications made by the transaction.

The specific syntax and operations may vary depending on the database system; the SQL statements in the above example are generic and should be adjusted according to the specific database system in actual use.

## 1. Background

In a database, a transaction refers to a series of database operations that are treated as a single execution unit. The goal of a transaction is to ensure the consistency and integrity of the database, allowing it to recover to its previous state even in the event of errors or interruptions. Transactions are typically used in scenarios where the atomicity of multiple database operations needs to be guaranteed.

- **When to Use Transactions**

1. Multi-step business operations:  
   When a business operation requires multiple steps to be executed, either all must succeed or all must fail, transactions can be used. For example, a bank transfer operation involves deducting an amount from one account and adding it to another; both steps must either succeed or fail together.

2. Ensuring data integrity:  
   When there are dependencies between multiple data operations that need to ensure data integrity, transactions can be used. For instance, in an order system, updating both order information and inventory information simultaneously requires that both operations either succeed or fail together.

3. Preventing concurrency issues:  
   In situations where multiple users access the database concurrently, data races and consistency issues may arise. Transactions can provide a locking mechanism to ensure that other transactions cannot modify the same data during the execution of one transaction.

## 2. Characteristics

- **Characteristics of Transactions**

1. Atomicity: A transaction is an atomic operation; it either fully succeeds or fully rolls back.

2. Consistency: The execution of a transaction moves the database from one consistent state to another.

3. Isolation: The execution of concurrent transactions does not interfere with each other; the data seen by each transaction during execution is independent.

4. Durability: Once a transaction is committed, its changes will be permanently saved in the database.

- **Problems Solved by Transactions**

1. Data consistency issues: Transactions ensure the atomicity of multiple operations, preventing data inconsistency issues that may arise from partial successes or failures.

2. Concurrency issues: Through the isolation of transactions, data races and consistency issues caused by concurrent execution of multiple transactions are prevented.

## 3. Example

Two student records will be inserted into a database table named student. If both insert operations are successfully executed, if either of the insert operations fails, the entire transaction will be rolled back, ensuring the consistency of the database. This approach guarantees that both insert operations either succeed simultaneously or fail simultaneously, thereby maintaining the integrity of the database.  
```  
await jianghuKnex.transaction(async trx => {  
    await trx('student').insert({ name: 'xxx1' });  
    await trx('student').insert({ name: 'xxx2' });  
});  
```

- **How to Use Database Transactions**

In most relational databases, the use of transactions typically involves the following steps:

1. Start the transaction: Initiate a new transaction by executing BEGIN TRANSACTION or a similar statement.

2. Execute transaction operations: Perform a series of database operations within the transaction, including data insertion, deletion, modification, and querying.

3. Commit the transaction: Execute the COMMIT statement to permanently save the changes of the transaction to the database.

4. Roll back the transaction: If an error or other unpredictable situation occurs during the execution of the transaction, the ROLLBACK statement can be executed to undo all modifications made by the transaction.

The specific syntax and operations may vary depending on the database system; the SQL statements in the above example are generic and should be adjusted according to the specific database system in actual use.