What is this?

A library providing a simple way of accessing a database and moving soft deleted rows to automatically generated tables and prevent performance erosion.
The library also allows the migration to happen on a different database.
Currently supported RDBMS are: Mysql, Sqlite.
Currently supported Node.js clients: mysql, mysql2, sqlite3.

How do I install it?

npm install soft-delete-migrator

How can I use it?

Use-case 1: Migrate soft deleted rows to the same database

Given a variable mySqlConn containing an active connection to a MySQL database, the following code will migrate all soft deleted rows from the users table to the users_deleted table considering all the deleted items prior to the 2022-12-31:

import { migrate } from 'soft-delete-migrator';

migrate(
  mySqlConn,
  {
    tableName: 'users',
    slaveTableName: 'users_deleted',
    softDeleteColumn: 'deleted_at',
    migrateCondition: 'deleted_at < ?',
    migrateConditionParams: ['2022-12-31'],
    limit: 500,
    chunkSize: 10,
    safeExecution: false,

  }
).then(() => {
  console.log('Migration completed');
}).catch((err) => {
  console.error('Migration failed', err);
});

Use-case 2: Migrate soft deleted rows to a different db connection/client

Given two variables, mySqlConn containing an active connection to a MySQL database and sqliteConn containing an active connection to a SQLite database, the following code will migrate all soft deleted rows from the users table of mySqlConn to the users_deleted table of sqliteConn considering all the deleted items prior to the 2022-12-31:

import { migrate } from 'soft-delete-migrator';

migrate(
  mySqlConn,
  {
    tableName: 'users',
    slaveTableName: 'users_deleted',
    softDeleteColumn: 'deleted_at',
    migrateCondition: 'deleted_at < ?',
    migrateConditionParams: ['2022-12-31'],
    limit: 500,
    chunkSize: 10,
    safeExecution: false,

  },
  sqliteConn
).then(() => {
  console.log('Migration completed');
}).catch((err) => {
  console.error('Migration failed', err);
});

API

A little introduction

When talking about a master database, we mean the database containing the table where the soft deleted rows will be migrated from.
When talking about a slave database, we mean the database containing the table where the soft deleted rows will be migrated to.
The slave database is optional. If not given, the library will create a table with the same name as the master table but with the _ prefix and the given/default schema.
This is similar to what the library does internally:

SELECT * FROM <schema>.<tableName> WHERE <softDeleteColumn> IS NOT NULL LIMIT <limit>

When talking about migrateCondition, we mean the condition to apply to the query to select the rows to migrate.
This condition will substitute the default one. Here's an example of what the library does internally:

SELECT * FROM <schema>.<tableName> WHERE <migrateCondition> LIMIT <limit>

migrate

The library exposes a migrate function, which executes the migration process.
The function expects the following parameters:

• masterConnection(required): The connection to the master database.
  The connection must be an instance of the following classes: mysql.Connection, mysql2.Connection, sqlite3.Database.
  The connection must be already connected as the library will not connect it.
• _config(required): An object containing the following properties:
  • tableName(required): The name of the master table containing the soft deleted rows.
  • schema(optional): The schema containing the table to migrate.
    Defaults to public.
  • softDeleteColumn(optional): The name of the column containing the soft delete datetime(MySQL) or timestamp (Sqlite).
    Defaults to deleted_at.
  • migrateCondition(optional): The condition to apply to the query to select the rows to migrate. This substitutes the WHERE clause in the query, ignoring the softDeleteColumn value. It supports the ? placeholder for parameters passed in migrateConditionParams. Defaults to 1=1.
  • migrateConditionParams(optional): The parameters to use in the migrateCondition query.
  • limit(optional): The maximum number of rows to migrate.
    Defaults to 1000.
  • chunkSize(optional): The number of rows to migrate at a time.
    Defaults to 100.
  • filePaths(optional): An array containing two file paths.
    The first file path is the path used to save the queries necessary for the master instance.
    The second file path is the path used to save the queries necessary for the slave instance.
  • safeExecution(optional): If set to true, the library will not execute the queries but will just write them to the filePaths, if given.
  • slaveSchema(optional): The schema containing the slave table.
    Defaults to undefined. If not set, the library will use the schema value.
  • slaveTableName(optional): The name of the slave table.
    Defaults to undefined. If not set, the library will use the tableName value with the _ prefix and the given/default schema.
  • closeConnectionOnFinish(optional): If set to true, the library will close the connection to the involved database(s) after the migration is completed.
  • autoRecoveryOnMappingError(optional): Usually, the library does a base64 encoding of the JSON stringification of all non-primary fields (All of them or just the passed columns). In case of error with any of those two processes, the library will throw an error. If set to true, in case of encoding error, the library will try to recover the data by mapping the fields only using the JSON stringification. In case of error in this phase, the library will save an empty string. Defaults to false.
  • onInsertedChunk(optional): A callback function to be called after each chunk of rows is inserted on the slave table.
  • onDeletedChunk(optional): A callback function to be called after each chunk of rows is deleted from the master table.
  • onInsertedChunkError(optional): A callback function to be called after each chunk of rows fails to be inserted on the slave table.
    Defaults to a function which throws the error.
  • onDeletedChunkError(optional): A callback function to be called after each chunk of rows fails to be deleted from the master table.
    Defaults to a function which throws the error.
• slaveConnection(optional): The connection to the slave database.
  If not given, the library will use the masterConnection for both the master and the slave database.

Other functions

The library also exposes two utility functions: getConnection and closeConnection.
The getConnection function expects the following parameters:

• client: The client to use.
  Can be either mysql, mysql2 or sqlite.
• config: The configuration to use to create the connection.
  • In case of mysql or mysql2, the configuration must be an instance of mysql.ConnectionConfig or mysql2.ConnectionOptions.
  • In case of sqlite, the configuration must be a string containing the path to the SQLite database.

FAQ

Why do I need to specify the schema?

The library uses the schema parameter to check, in case of MySql, if the table exists in the information schema tables.

How can you ensure data integrity?

The library does all of its work in a transaction.
If the migration fails, the transaction is rolled back and the data is not migrated.
If the migration succeeds, the transaction is committed and the data is migrated.

How can you ensure that the migration is not executed twice?

The library is idempotent in itself as it just considers the rows respecting the NOT NULL value of the softDeleteColumn or the migrateCondition, if passed.
If you want to ensure that the migration is not executed twice, you can use the filePaths configuration to save the queries necessary to execute the migration, set the safeExecution configuration to true and then execute them manually.

Tests

You can run the tests by using the following command:

npm test

As the tests are using a real database, you need to have a MySQL running on your machine.
You can configure the connection details in the test/shared.ts file.
The MySQL instance must have two schemas already created: soft_delete_migrator and soft_delete_migrator_slave.
The SQLite instances are created in memory and do not need any configuration.

ToDo

• [ ] Try to understand if schema can be removed. Maybe tell dev to specify it or take from connection?
• [ ] Integrity mechanism to check if primary keys exist both in master and slave table.
• [ ] Add support for other databases. Maybe suggest a generic connection interface?
• [ ] Refactor using adapters.