Apache Velocity Templating Example

SchemaCrawler integrates with Apache Velocity to allow you to generate custom text output from your database schema using Velocity templates. You can use the full Velocity Template Language (VTL) to iterate over schemas, tables, and columns and produce any text format you need.

How to Run

Before running this example, complete the setup in Getting Started.

1. Create a file called “tables.vm” with the contents shown below.
2. Run the command:

schemacrawler \
  --server postgresql \
  --host postgresql \
  --database schemacrawler \
  --user schemacrawler \
  --password schemacrawler \
  --info-level standard \
  --command template \
  --templating-language=velocity \
  --template share/tables.vm \
  --output-file share/output.txt

Replace with the connection options for your chosen database. See Getting Started.

The output file will appear in your current working directory on the host.

Resource Files

tables.vm

$catalog.crawlInfo

#foreach($schema in $catalog.schemas)
SET SCHEMA $schema.fullName;

#foreach($table in $catalog.getTables($schema))
#if ($table.tableType == "table")
CREATE TABLE $identifiers.quoteName($table)
(
  #foreach($column in $table.columns)
    $identifiers.quoteName($column) $column.columnDataType#if(!$column.isNullable()) NOT NULL#end#if($foreach.count < $table.columns.size()),#end
  #end
);

#end
#end
#end

Place this file in your working directory. It will be accessible inside the container as share/tables.vm.

How to Experiment

1. Modify tables.vm to change the output format — for example, produce HTML, CSV, or a custom SQL dialect.
2. Pass a different .vm template file via --template share/<filename>.vm to try alternate templates.
3. Explore other Velocity variables available on the $catalog object, such as $catalog.tables, to access additional schema metadata.
4. Adjust the --info-level flag (e.g., detailed or maximum) in the script to expose more schema information to the template.