Calling Commands

Overview

The liquibase.command.CommandScope class is the primary high-level facade for running Liquibase operations.

The API provides both a way to call individual commands and metadata about each command including human-readable descriptions and argument information.

The operations available through the command API are end-user facing, complete calls such as "update", "rollback", or "generateChangelog".

How to use Command Framework

The main components from Command framework are described below.

Command Name

This is just a constant where we will define the known names for a given command.

public static String[] COMMAND_NAME = {"update"};

Similarly, for certain commands there could be a legacy command name which can be defined in the same way and be passed to the CommandBuilder constructor.

Arguments

There are required and optional arguments used by a command that are defined in the below way. Either in the code or documentation you can see what is each command for and whether it's required or not.

static {

        public static final String[] LEGACY_COMMAND_NAME = {"migrate"};
        public static String[] COMMAND_NAME = {"update"};

        public static final CommandArgumentDefinition<String> CHANGELOG_FILE_ARG;

        public static final CommandArgumentDefinition<DatabaseChangeLog> CHANGELOG_ARG;
        public static final CommandArgumentDefinition<String> LABEL_FILTER_ARG;
        public static final CommandArgumentDefinition<String> CONTEXTS_ARG;

        CommandBuilder builder = new CommandBuilder(COMMAND_NAME, LEGACY_COMMAND_NAME);
        CHANGELOG_ARG = builder.argument("databaseChangelog", DatabaseChangeLog.class).hidden().build();
        CHANGELOG_FILE_ARG = builder.argument(CommonArgumentNames.CHANGELOG_FILE, String.class)
                .required().description("The root changelog").supersededBy(CHANGELOG_ARG).build();
        CHANGELOG_ARG.setSupersededBy(CHANGELOG_FILE_ARG);
        LABEL_FILTER_ARG = builder.argument("labelFilter", String.class)
                .addAlias("labels")
                .description("Changeset labels to match")
                .build();
        CONTEXTS_ARG = builder.argument("contextFilter", String.class)
                .addAlias("contexts")
                .description("Changeset contexts to match")
                .build();
    }

Additionally, we can also specify some other generic argument, for example a outputStream were command results will be written into. Below an example of it:

CommandScope updateCommand = new CommandScope(UpdateSqlCommandStep.COMMAND_NAME);
        ...
updateCommand.setOutput(new WriterOutputStream(output, GlobalConfiguration.OUTPUT_FILE_ENCODING.getCurrentValue()));
updateCommand.execute();

Dependencies

Dependencies are not useful for calling a command, but they are useful when defining a new command. These specified dependencies are basically part of the different stages of the pipeline execution for a given command.

@Override
    public List<Class<?>> requiredDependencies() {
        List<Class<?>> deps = Arrays.asList(Database.class, DatabaseChangeLog.class, 
        ChangeExecListener.class, ChangeLogParameters.class, UpdateSummaryEnum.class);
        return deps;
    }

What we need to understand here is the above dependencies classes will execute their own run() method which is needed to accomplish with the run() of the given command, for example update command.

Execution

Each command step class will need to implement their own run() method. Basically, this method will have the main business logic of a given command/component.

@Override
    public void run(CommandResultsBuilder resultsBuilder) throws Exception {
        setDBLock(false);
        super.run(resultsBuilder);
    }

This method will be called by invoking the CommandScope execute() method as shown below:

CommandScope updateCommand = new CommandScope("update");
        updateCommand.addArgumentValue(UpdateCommandStep.CHANGELOG_FILE_ARG, changeLogFile);
        ...
        updateCommand.execute();

Command Execution examples

Regular use execution example

package com.example;

import liquibase.command.CommandScope;
import liquibase.exception.CommandExecutionException;

public class ExampleIntegration  {

    public static void main(String[] args) throws Exception {
        // ... setup configuration system and file access

        try {
            CommandScope updateCommand = new CommandScope("update");
            updateCommand.addArgumentValue(UpdateCommandStep.CHANGELOG_FILE_ARG, changeLogFile);
            updateCommand.addArgumentValue(UpdateCommandStep.CONTEXTS_ARG, contexts);
            updateCommand.addArgumentValue(UpdateCommandStep.LABEL_FILTER_ARG, labelFilter);
            updateCommand.addArgumentValue(ChangeExecListenerCommandStep.CHANGE_EXEC_LISTENER_CLASS_ARG, changeExecListenerClass);
            updateCommand.addArgumentValue(ChangeExecListenerCommandStep.CHANGE_EXEC_LISTENER_PROPERTIES_FILE_ARG, changeExecListenerPropertiesFile);
            setDatabaseArgumentsToCommand(updateCommand);
            updateCommand.execute();
        } catch (CommandExecutionException e) {
            System.out.println("Error running update: "+e.getMessage());
        }
    }
}

Execution in scope example

A scope refers to an environment where a given set of operations happen. For example, in the context of CLI, a Scope refers to the environment where the operations will be executed. The two scopes are parent and child.

In the child scope, we could group and execute additional operations with the benefit that variables or objects from the parent scope are accessible in the child scope.

In this example, the files are defined in the parent scope and are available to the commands in the child scope shown below.

Map<String, Object> scopedSettings = new LinkedHashMap<>();
scopedSettings.put(Scope.Attr.resourceAccessor.name(), resourceAccessor);
Scope.child(scopeSettings, () {
  CommandScope commandScope = new CommandScope(UpdateCommandStep.COMMAND_NAME);
  commandScope.addArgumentValue(DbUrlConnectionCommandStep.URL_ARG, db.getConnectionUrl());
  commandScope.addArgumentValue(DbUrlConnectionCommandStep.USERNAME_ARG, db.getUsername());
  commandScope.addArgumentValue(DbUrlConnectionCommandStep.PASSWORD_ARG, db.getPassword());
  commandScope.addArgumentValue(UpdateCommandStep.CHANGELOG_FILE_ARG, changelogFile);
  commandScope.addArgumentValue(ShowSummaryArgument.SHOW_SUMMARY, UpdateSummaryEnum.SUMMARY);
  commandScope.execute();
}); 

API Documentation

For a complete description of the CommandScope API, including methods to call, see liquibase.command.CommandScope.