FWD » Core Development » Database

package com.goldencode.p2j.persist.orm;

import com.goldencode.p2j.persist.Database;

import com.goldencode.p2j.persist.PersistenceException;

import java.io.IOException;

import java.sql.Connection;

import java.util.ArrayList;

import java.util.List;

/**

 * JDBC schema comparator. Compares current DB schema state with last known state. Last known state may be provided.

 */

public class SchemaComparator {

    /**

     * Get an instance of the Comparator, load the current database state for use in comparison.

     *

     * @param database database to connect to

     * @return Comparator instance

     */

    public static SchemaComparator saveInitialState(Database database) {

        SchemaComparator schemaComparator = new SchemaComparator(database);

        schemaComparator.saveLastKnownState(null);

        return schemaComparator;

    }

    /**

     * Get an instance of the Comparator, assuming the current database state is already loaded.

     *

     * @param database database to connect to

     * @return Comparator instance

     */

    public static SchemaComparator getInstanceExistingState(Database database) {

        return new SchemaComparator(database);

    }

    private final Database database;

    private SchemaComparator(Database database) {

        this.database = database;

    }

    /**

     * Compare current state with last known state.

     *

     * @return ComparisonResult instance

     * @throws IOException translated from PersistenceException

     */

    public ComparisonResult compareWithPrevious() throws IOException {

        Object previousState = loadLastKnownState();

        return compare(previousState);

    }

    /**

     * Compare current state with given state.

     *

     * @param previousState previous known state for comparison

     * @return ComparisonResult instance

     * @throws IOException translated from PersistenceException

     */

    // TODO: use specific type for previousState

    public ComparisonResult compare(Object previousState) throws IOException {

        try (Session session = new Session(database))

        {

            Connection conn = session.getConnection();

            ComparisonResult comparisonResult = new ComparisonResult();

            getAndCompareTables(conn, previousState, comparisonResult);

            getAndCompareColumns(conn, previousState, comparisonResult);

            getAndCompareIndexes(conn, previousState, comparisonResult);

            if (!comparisonResult.isSame())

            {

                saveLastKnownState(comparisonResult.getState());

            }

            return comparisonResult;

        } catch (PersistenceException e) {

            throw new IOException("Connection failed during comparison", e);

        }

    }

    private Object loadLastKnownState() {

        // TODO

        return null;

    }

    private void saveLastKnownState(Object newState) {

        // TODO: persist state info

    }

    private void getAndCompareTables(Connection conn, Object previousState, ComparisonResult comparisonResult) {

        // TODO: load info from conn

        if (previousState != null)

        {

            // TODO: compare with previous state

        }

        // TODO: fill comparison result

    }

    private void getAndCompareColumns(Connection conn, Object previousState, ComparisonResult comparisonResult) {

        // TODO: load info from conn

        if (previousState != null)

        {

            // TODO: compare with previous state

        }

        // TODO: fill comparison result

    }

    private void getAndCompareIndexes(Connection conn, Object previousState, ComparisonResult comparisonResult) {

        // TODO: load info from conn

        if (previousState != null)

        {

            // TODO: compare with previous state

        }

        // TODO: fill comparison result

    }

    /**

     * Result of schema comparison.

     *

     * TODO: could be immutable, requires builder

     */

    public static class ComparisonResult {

        private Object state = null;

        private List<Object> differences = new ArrayList<>();

        public boolean isSame() {

            return differences.isEmpty();

        }

        public List<Object> getDifferences() {

            return differences;

        }

        private Object getState() {

            return state;

        }

    }

}