Create an ER Diagram of an Existing SQLite Database (or many other RDBMS)
Visualisation helps solving problems and is therefore an important tool database design. Many database providers have their product specific tools for re-engineering existing schemata, but self-contained, serverless, embedded relational database management systems (RDBMS) such as SQLite often come without much tooling support. The extremely small footprint of SQLite provides a very powerful tool for implementing database driven applications without the hassle of database administration, user privilege management and other demanding tasks that come with more complex systems. There does not exist a workbench-like tool for SQLite, but we can use the open source SchemaCrawler for analysing database schemata and table relationships. The tool provides a plethora of commands and options, in this post we will only cover the diagramming part, which allows creating ER diagrams of the table.
After downloading and extracting the tool to your local drive, you can find a lot of examples included. The tool can handle SQLite, Oracle, MS SQL Server, IBM DB2, MySQL, MariaDB, Postgres and Sybase database servers and is therefore very versatile. You will need Java 8 in order to run it. Have a look at the script below, which creates a PNG image of the database schema of the Chinook test database.
#!/bin/bash
# The path of the unzipped SchemaCrawler directory
SchemaCrawlerPATH=/media/stefan/Datenbank/schemacrawler-14.05.04-main
# The path of the SQLite database
SQLiteDatabaseFILE=/media/stefan/Datenbank/ChinookDatabase1.4_CompleteVersion/Chinook_Sqlite.sqlite
# The type of the database system.
RDBMS=sqlite
# Where to store the image
OutputPATH=/media/stefan/Datenbank/ER.png
# Username and password need to be empty for SQLite
USER=
PASSWORD=
java -classpath $(echo ${SchemaCrawlerPATH}/_schemacrawler/lib/*.jar | tr ' ' ':') schemacrawler.Main -server=${RDBMS} -database=${SQLiteDatabaseFILE} -outputformat=png -outputfile=${OutputPATH} -command=graph -infolevel=maximum -user=${USER} -password=${PASSWORD}
The SchemaCrawlerPATH variable contains the path to the directory where we unzipped the SchemaCrawler files to. This is needed in order to load all the required libraries into the classpath below. We then specify the SQLite database file, define the RDBMS and provide an output path where we store the image. Additionally, we provide an empty user name and password combination. SQLite does not provide user authentication, thus those two parameters need to be empty, SchemaCrawler simply ignores them. Then we can execute the command and the tool generates the PNG of the ER diagram for us.
You can find a lot of examples also online, which gives you an overview of the features of this tool. One of the main purposes of SchemaCrawler is to generate diffable text outputs of the database schemata. In combination with a source code version management tool such as Git or Subversion, you can create clean and usable reports of your databases and keep track of the changes there. You can retrieve an overview of the options with the following command.
java -classpath $(echo ${SchemaCrawlerPATH}/_schemacrawler/lib/*.jar | tr ' ' ':') schemacrawler.Main -?
You can also HTML reports with the following command:
java -classpath $(echo ${SchemaCrawlerPATH}/_schemacrawler/lib/*.jar | tr ' ' ':') schemacrawler.Main -server=${RDBMS} -database=${SQLiteDatabaseFILE} -outputformat=html -outputfile=report.html -command=details -infolevel=maximum -user=${USER} -password=${PASSWORD}
Other available output formats are plain text, CSV or JSON.