SchemaCrawler

SchemaCrawler is a free database schema discovery and comprehension tool. SchemaCrawler has a good mix useful features for data governance. You can search for database schema objects using regular expressions, and output the schema and data in a readable text format. The output serves for database documentation, and is designed to be diff-ed against other database schemas. SchemaCrawler also generates schema diagrams. You can execute scripts in any standard scripting language against your database. You can find potential schema design issues with lint.

SchemaCrawler supports almost any database that has a JDBC driver, but for convenience is bundled with drivers for some commonly used RDBMS systems. SchemaCrawler works with any operating system that supports Java 7 or better.

SchemaCrawler API

SchemaCrawler is also a Java API that makes working with database metadata as easy as working with plain old Java objects. Java programmers need to access database metadata

• in order to dynamically generate SQL statements
• when programmatically determining the capabilities of a given RDBMS
• when finding the names and types of tables and columns in the database

Programmers can obtain database metadata using JDBC, but with the raw JDBC API database metadata is returned as result sets, not Java objects. Also, programmers are still responsible for managing resources, mapping into object structures, and handling exceptions. This makes using the JDBC API very cumbersome when it comes to metadata. Furthermore, the JDBC API is not very consistent. For example, to find the type of a table, you would look at the TABLE_TYPE , which has a string value, but for procedures, PROCEDURE_TYPE is an integer. An another example, is the getCatalogs() call, which returns a result set with exactly one column, in contrast to getStringFunctions() which returns a string containing the list of function names, separated by commas.

SchemaCrawler attempts to solve some of these problems by providing an API that is consistent and usable. Database metadata is provided in the form of plain old Java objects (POJOs). Some examples of the consistency and usability of the SchemaCrawler API are that:

• Table is an object that has a collection of Column objects, without requiring you to make additional calls
• Booleans are Java booleans, not an integer, a string, or null versus not-null, and enumerated values are Java enums, not integers
• Lists are always Java lists - java.util.List
• You don't worry about database resources or exception handling
• You can use standard Java programming idioms - for example, you can access the Table object from a Column object using getParent()

SchemaCrawler goes beyond what is available using JDBC, and can provide information on database triggers and database synonyms as well.

SchemaCrawler is free and open-source API available under the LGPL license. SchemaCrawler is written in Java, making it operating system agnostic. Since it leverages JDBC, it is also database independent. It deliberately doesn't have any RDBMS-specific code. SchemaCrawler allows you to compare structures between two different database servers, or even two different database systems, from different vendors.

The sample code below demonstrates just how easy it is to use SchemaCrawler:

final SchemaCrawlerOptions options = new SchemaCrawlerOptions();
// Set what details are required in the schema - this affects the
// time taken to crawl the schema
options.setSchemaInfoLevel(SchemaInfoLevel.standard());

final Database database = SchemaCrawlerUtility.getDatabase(connection, options);
for (final Schema schema: database.getSchemas())
{
  System.out.println(schema);
  for (final Table table: database.getTables(schema))
  {
    System.out.print("o--> " + table);
    for (final Column column: table.getColumns())
    {
      System.out.println("     o--> " + column);
    }
  }
}
    

SchemaCrawler Command Line

SchemaCrawler comes with a set of command line tools that allow database metadata to be output as plain text, comma-separated text (CSV), HTML5, or JavaScript object notation (JSON). The HTML5 output is a combination of valid XML (that can be manipulated by XML tools or XSLT), and HTML that can be viewed in a browser. All formats are designed to be easy to diff , or find differences with other schemas that may have been output in the same format.

SchemaCrawler has grep functionality that allows you to search for table and column names using regular expressions. SchemaCrawler is capable of creating entity-relationship diagrams in DOT format, which GraphViz can convert into schema diagrams. SchemaCrawler has powerful scripting ability, using JavaScript, Groovy, Ruby or Python. A live connection is provided to the script context to allow you to select from or even modify your database. Examples are provided for all of these with the download .

SchemaCrawler is integrated with, and allows you to write templates to generate SQL scripts or any other text output, using templating engines, such as Apache Velocity or <FreeMarker> . However, you will need to download Apache Velocity or <FreeMarker> separately, since these are not part of the SchemaCrawler download.