kern/src/de/superx/util/db/PostgresMetadataHelper.java

package de.superx.util.db;

import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;

import de.superx.rest.model.TableInfo;
import de.superx.rest.model.TableInfo.ColumnInfo;

public class PostgresMetadataHelper {
    private final Connection connection;

    public PostgresMetadataHelper(Connection connection) {
        this.connection = connection;
    }

    public List<TableInfo> getTablesWithComments(String schema, boolean withColumns) throws SQLException {
        return getTablesWithComments(schema, "%", withColumns);
    }
    
    public List<TableInfo> getTablesWithComments(String schema, String tableFilter, boolean withColumns) throws SQLException {
        List<TableInfo> tables = new ArrayList<>();

        // Get tables via DatabaseMetaData
        DatabaseMetaData meta = connection.getMetaData();
        ResultSet tableRs = meta.getTables(null, schema, tableFilter, new String[]{"TABLE"});

        while (tableRs.next()) {
            String tableName = tableRs.getString("TABLE_NAME");

            // Get table comment via PostgreSQL catalog
            String comment = getTableComment(schema, tableName);
            
            int rowCount = 0;
            
            try (Statement st = connection.createStatement(); ResultSet rs = st.executeQuery(String.format("SELECT COUNT(*) FROM %s.%s", schema, tableName))) {
                rs.next();
                rowCount = rs.getInt(1);
            }

            TableInfo info = new TableInfo(tableName, schema, comment, Integer.valueOf(rowCount));
            if (withColumns) {
                // Get columns
                ResultSet colRs = meta.getColumns(null, schema, tableName, "%");
                List<ColumnInfo> columns = new ArrayList<>();
                while (colRs.next()) {
                    ColumnInfo col = new ColumnInfo();
                    col.name = colRs.getString("COLUMN_NAME");
                    col.typeName = colRs.getString("TYPE_NAME");
                    col.size = colRs.getInt("COLUMN_SIZE");
                    col.nullable = colRs.getInt("NULLABLE") == DatabaseMetaData.columnNullable;
                    col.defaultValue = colRs.getString("COLUMN_DEF");
                    col.comment = getColumnComment(schema, tableName, col.name);
                    columns.add(col);
                }
                colRs.close();
                info.setColumns(columns);
            }
            tables.add(info);
        }
        tableRs.close();
        return tables;
    }

    private String getTableComment(String schema, String table) throws SQLException {
        String sql = """
                        SELECT d.description 
                        FROM pg_class c
                        JOIN pg_namespace n ON n.oid = c.relnamespace
                        LEFT JOIN pg_description d ON d.objoid = c.oid AND d.objsubid = 0
                        WHERE c.relname = ? AND n.nspname = ?
                        """;
        try (PreparedStatement stmt = connection.prepareStatement(sql)) {
            stmt.setString(1, table);
            stmt.setString(2, schema);
            try (ResultSet rs = stmt.executeQuery()) {
                return rs.next() ? rs.getString(1) : null;
            }
        }
    }

    private String getColumnComment(String schema, String table, String column) throws SQLException {
        String sql = """
                        SELECT d.description 
                        FROM pg_class c
                        JOIN pg_namespace n ON n.oid = c.relnamespace
                        JOIN pg_attribute a ON a.attrelid = c.oid
                        LEFT JOIN pg_description d ON d.objoid = a.attrelid AND d.objsubid = a.attnum
                        WHERE c.relname = ? AND n.nspname = ? AND a.attname = ?
                        """;
        try (PreparedStatement stmt = connection.prepareStatement(sql)) {
            stmt.setString(1, table);
            stmt.setString(2, schema);
            stmt.setString(3, column);
            try (ResultSet rs = stmt.executeQuery()) {
                return rs.next() ? rs.getString(1) : null;
            }
        }
    }
}