Write to a Database Using Merge Upsert Strategy

Updated: Jan 22, 2023

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This example shows you how to upsert records to a database using Data Pipeline's JdbcUpsertWriter and MergeUpsert.

Upsert(a portmanteau of update and insert) is a database operation that will update an existing row if a specified value already exists in a table, and insert a new row if the specified value doesn't already exist. Data Pipeline provides several upsert strategies such as GenericUpsert, MergeUpsert,MySqlUpsert and others.

Upsert strategies available in Data Pipeline allows you to choose a strategy which is supported by the database management system you are using. For example MergeUpsert is supported by Oracle Database, MS SQL, IBM Db2, Teradata, Firebird, H2, HSQLDB , Apache Derby and some other database management systems.

Java Code listing

package com.northconcepts.datapipeline.examples.cookbook;

import java.io.File;
import java.io.OutputStreamWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;

import com.northconcepts.datapipeline.core.DataException;
import com.northconcepts.datapipeline.core.DataReader;
import com.northconcepts.datapipeline.core.DataWriter;
import com.northconcepts.datapipeline.csv.CSVReader;
import com.northconcepts.datapipeline.csv.CSVWriter;
import com.northconcepts.datapipeline.jdbc.JdbcReader;
import com.northconcepts.datapipeline.jdbc.JdbcUpsertWriter;
import com.northconcepts.datapipeline.jdbc.upsert.MergeUpsert;
import com.northconcepts.datapipeline.job.Job;

public class WriteToDatabaseUsingMergeUpsert {

	public static void main(String[] args) {

		final String DATABASE_DRIVER = "org.hsqldb.jdbcDriver";
		final String DATABASE_URL = "jdbc:hsqldb:mem:aname";
		final String DATABASE_USERNAME = "sa";
		final String DATABASE_PASSWORD = "";
		final String DATABASE_TABLE = "CreditBalance";
		final String PRIMARY_KEY = "Account";

		Connection connection;
		try {
			Class.forName(DATABASE_DRIVER);
			connection = DriverManager.getConnection(DATABASE_URL, DATABASE_USERNAME, DATABASE_PASSWORD);

			createTable(connection);
		} catch (Throwable e) {
			throw DataException.wrap(e);
		}

		DataReader reader = new CSVReader(new File("example/data/input/credit-balance-upsert-records.csv")).setFieldNamesInFirstRow(true);
		DataWriter writer = new JdbcUpsertWriter(connection, DATABASE_TABLE, new MergeUpsert().setDebug(true), PRIMARY_KEY);

		Job.run(reader, writer);

		reader = new JdbcReader(connection, "Select * from CreditBalance;");
		writer = new CSVWriter(new OutputStreamWriter(System.out));

		Job.run(reader, writer);
	}

	public static void createTable(Connection connection) throws Throwable{
		PreparedStatement preparedStatement;
		String dropTableQuery = "DROP TABLE CreditBalance IF EXISTS;";
		String createTableQuery = "CREATE TABLE CreditBalance ("
			+ "Account INTEGER, "
			+ "LastName VARCHAR(256), "
			+ "FirstName VARCHAR(256), "
			+ "Balance DOUBLE, "
			+ "CreditLimit DOUBLE, "
			+ "AccountCreated DATE, "
			+ "Rating CHAR, "
			+ "PRIMARY KEY (Account));";

		preparedStatement = connection.prepareStatement(dropTableQuery);
		preparedStatement.execute();

		preparedStatement = connection.prepareStatement(createTableQuery);
		preparedStatement.execute();
	}
}

Code walkthrough

1. First, database connection parameters are specified.
2. Class.forName() is used to register a database driver. In this example hsqldb.jdbcDriver is registered.
3. A method createTable() creates a table CreditBalance in your database( drops it first if it already exists).
4. CSVReader is created corresponding to an input file credit-balance-upsert-records.csv.
5. setFieldNamesInFirstRow(true) is invoked to specify that the names specified in the first row should be used as field names (disabled by default). If this method is not invoked, the fields would be named as A1, A2 by default.
6. JdbcUpsertWriter is created to upsert records to a database using MergeUpsert strategy. A key field name PRIMARY_KEY in the parameter indicates that Account column will be used as key to determine whether a record already exists in the table.
7. setDebug(true) enables the MergeUpsert to log the generated SQL(disabled by default).
8. Data are transferred from CSVReader to JdbcUpsertWriter via Job.run() method to populate or update your database table with records obtained from the CSV file .
9. JdbcReader is created to obtain records from the specified database.
10. CSVWriter is created to write records to a CSV stream.
11. Data are transferred from JdbcReader to CSVWriter via Job.run() method. See how to compile and run data pipeline jobs.

JdbcUpsertWriter

Writes records to a database table using the upsert idiom (attempt to insert, but update if duplicate key exists). The default strategy used is GenericUpsert, however several other are provided: MergeUpsert, VariableFieldsUpsert, MySqlUpsert.

MergeUpsert

A batch-able upsert strategy that relies on the SQL Merge statement. A method setDebug() allows MergeUpsert to log the generated SQL(disabled by default). For this example the generated SQL will look something like this

• MERGE INTO CreditBalance target USING (VALUES (?)) source(Account) ON target.Account=source.Account WHEN NOT MATCHED THEN INSERT (col1, col2, col3) VALUES (?, ?, ?) WHEN MATCHED THEN UPDATE SET SET col1=?, col2=?, col3=?;

JdbcReader

Obtains records from a database query. It extends DataReader class and it's constructor takes Connection object and query string as a parameter.

CSVReader

Obtains records from a Comma Separated Value (CSV) or delimited stream. It extends TextReader class and can be created using or Reader object. Passing true to method setFieldNamesInFirstRow() in this class enables the CSVReader to use the names specified in the first row of the input data as field names.

CSVWriter

Writes records to a Comma Separated Value (CSV) stream. It extends LinedTextWriter and it's constructor takes a File or a Writer object as parameter.

Console Output

Obtained records will be printed on the console.