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springboot启动初始化ddl过程

跟踪Springboot整合hibernate的启动代码：

SessionFactoryImpl 的初始化里做了非常多的事情，初始化各种资源，并调用 SchemaManagementToolCoordinator.process 先执行脚本任务再执行 Db任务：

		performScriptAction( actions.getScriptAction(), metadata, tool, serviceRegistry, executionOptions, configService );performDatabaseAction( actions.getDatabaseAction(), metadata, tool, serviceRegistry, executionOptions );

在这里就开始进行 spring.jpa.hibernate.ddl-auto 配置的项，进行处理了。

在 doMigration 时，就获取到 tables 的元数据：

public class GroupedSchemaMigratorImpl extends AbstractSchemaMigrator {public GroupedSchemaMigratorImpl(HibernateSchemaManagementTool tool, SchemaFilter schemaFilter) {super(tool, schemaFilter);}protected NameSpaceTablesInformation performTablesMigration(Metadata metadata, DatabaseInformation existingDatabase, ExecutionOptions options, Dialect dialect, Formatter formatter, Set<String> exportIdentifiers, boolean tryToCreateCatalogs, boolean tryToCreateSchemas, Set<Identifier> exportedCatalogs, Namespace namespace, GenerationTarget[] targets) {NameSpaceTablesInformation tablesInformation = new NameSpaceTablesInformation(metadata.getDatabase().getJdbcEnvironment().getIdentifierHelper());if (this.schemaFilter.includeNamespace(namespace)) {this.createSchemaAndCatalog(existingDatabase, options, dialect, formatter, tryToCreateCatalogs, tryToCreateSchemas, exportedCatalogs, namespace, targets);NameSpaceTablesInformation tables = existingDatabase.getTablesInformation(namespace);Iterator var14 = namespace.getTables().iterator();Table table;TableInformation tableInformation;while(var14.hasNext()) {table = (Table)var14.next();if (this.schemaFilter.includeTable(table) && table.isPhysicalTable()) {this.checkExportIdentifier(table, exportIdentifiers);tableInformation = tables.getTableInformation(table);if (tableInformation == null) {this.createTable(table, dialect, metadata, formatter, options, targets);} else if (tableInformation != null && tableInformation.isPhysicalTable()) {tablesInformation.addTableInformation(tableInformation);this.migrateTable(table, tableInformation, dialect, metadata, formatter, options, targets);}}}var14 = namespace.getTables().iterator();while(true) {do {do {do {if (!var14.hasNext()) {return tablesInformation;}table = (Table)var14.next();} while(!this.schemaFilter.includeTable(table));} while(!table.isPhysicalTable());tableInformation = tablesInformation.getTableInformation(table);} while(tableInformation != null && (tableInformation == null || !tableInformation.isPhysicalTable()));this.applyIndexes(table, tableInformation, dialect, metadata, formatter, options, targets);this.applyUniqueKeys(table, tableInformation, dialect, metadata, formatter, options, targets);}} else {return tablesInformation;}}
}

如何自定义修改 table

再往下的过程，到 HibernateSchemaManagementTool 这个核心类：

ddl-auto 语义的实现，就在这里。
那要自定义修改 table ，最常见的需要就是 hibernate 只能增加，对于修改字段长度这一类的涉及不到。当然这种修改只限于开发技术交流，生产环境慎用。
回归正题，要想修改字段长度有这么几个关键数据：

• table 的元数据
• Entity 的元数据
  hibernate 本身的功能，如 Migrator 既然能识别到字段缺失，那肯定也能获取到这2个元数据。也就是2个参数：registry 和 metadata。
  了解了需要的数据，就有了思路：

public void migrateDB(DataSourceProperties dataSource, EntityManager entityManager, String ddlAuto, String dialectStr) {log.info("schema 生成：{}", dataSource.getUrl());Set<EntityType<?>> entities = entityManager.getMetamodel().getEntities();Properties p = new Properties();// 数据库方言，最终输出的方言p.put(AvailableSettings.DIALECT, dialectStr);// 自动执行的动作p.put(AvailableSettings.HBM2DDL_AUTO, ddlAuto);// 分隔符，默认为空p.put(AvailableSettings.HBM2DDL_DELIMITER, ";");// 是否展示SQLp.put(AvailableSettings.SHOW_SQL, true);p.put("hibernate.connection.driver_class", dataSource.getDriverClassName());p.put("hibernate.connection.url", dataSource.getUrl());p.put("hibernate.connection.username", dataSource.getUsername());p.put("hibernate.connection.password", dataSource.getPassword());// 是否使用默认的jdbc元数据，默认为true，读取项目自身的元数据p.put("hibernate.temp.use_jdbc_metadata_defaults", true);
//                p.put("hibernate.temp.use_jdbc_metadata_defaults", false);ConfigurationHelper.resolvePlaceHolders(p);try (ServiceRegistry registry = new StandardServiceRegistryBuilder().applySettings(p).build()) {Map settings = registry.getService(ConfigurationService.class).getSettings();MetadataSources metadataSources = new MetadataSources(registry);entities.forEach(entityType -> metadataSources.addAnnotatedClass(entityType.getJavaType()));Metadata metadata = metadataSources.buildMetadata();HashMap properties = new HashMap<>();properties.putAll(registry.getService(ConfigurationService.class).getSettings());log.info("开始migration");SchemaManagementToolCoordinator.process(metadata, registry, settings, null);log.info("开始alter migration");SchemaAlterTool schemaAlterTool = new SchemaAlterTool(registry);schemaAlterTool.performTablesAlter(registry, metadata);}}public void migrateDB(String jdbcUrl, DataSourceProperties dataSource, Set<EntityType<?>> entities, String ddlAuto) {log.info("schema 生成：{}", jdbcUrl);Properties p = new Properties();// 数据库方言，最终输出的方言p.put(AvailableSettings.DIALECT, MySQL5InnoDBDialect.class.getName());// 自动执行的动作p.put(AvailableSettings.HBM2DDL_AUTO, ddlAuto);// 分隔符，默认为空p.put(AvailableSettings.HBM2DDL_DELIMITER, ";");// 是否展示SQLp.put(AvailableSettings.SHOW_SQL, true);p.put("hibernate.connection.driver_class", dataSource.getDriverClassName());p.put("hibernate.connection.url", jdbcUrl);p.put("hibernate.connection.username", dataSource.getUsername());p.put("hibernate.connection.password", dataSource.getPassword());// 是否使用默认的jdbc元数据，默认为true，读取项目自身的元数据p.put("hibernate.temp.use_jdbc_metadata_defaults", true);
//                p.put("hibernate.temp.use_jdbc_metadata_defaults", false);ConfigurationHelper.resolvePlaceHolders(p);try (ServiceRegistry registry = new StandardServiceRegistryBuilder().applySettings(p).build()) {Map settings = registry.getService(ConfigurationService.class).getSettings();MetadataSources metadataSources = new MetadataSources(registry);entities.forEach(entityType -> metadataSources.addAnnotatedClass(entityType.getJavaType()));Metadata metadata = metadataSources.buildMetadata();HashMap properties = new HashMap<>();properties.putAll(registry.getService(ConfigurationService.class).getSettings());log.info("开始migration");SchemaManagementToolCoordinator.process(metadata, registry, settings, null);log.info("开始alter migration");SchemaAlterTool schemaAlterTool = new SchemaAlterTool(registry);schemaAlterTool.performTablesAlter(registry, metadata);}}

自定义 hibernate 的entity 关联 table：

public class SchemaAlterTool {private Logger log = LoggerFactory.getLogger(SchemaAlterTool.class);protected SchemaFilter schemaFilter;ServiceRegistry registry;private HibernateSchemaManagementTool tool;private JdbcContext jdbcContext;public SchemaAlterTool(ServiceRegistry registry) {this.registry = registry;SchemaFilterProvider schemaFilterProvider = registry.getService(StrategySelector.class).resolveDefaultableStrategy(SchemaFilterProvider.class,null,DefaultSchemaFilterProvider.INSTANCE);this.schemaFilter = schemaFilterProvider.getMigrateFilter();}protected void validateColumnType(Table table, Column column, ColumnInformation columnInformation, Metadata metadata, Dialect dialect) {boolean typesMatch = column.getSqlTypeCode(metadata) == columnInformation.getTypeCode() || column.getSqlType(dialect, metadata).toLowerCase(Locale.ROOT).startsWith(columnInformation.getTypeName().toLowerCase(Locale.ROOT));if (!typesMatch) {throw new SchemaManagementException(String.format("Schema-alter: wrong column type encountered in column [%s] in table [%s]; found [%s (Types#%s)], but expecting [%s (Types#%s)]", column.getName(), table.getQualifiedTableName(), columnInformation.getTypeName().toLowerCase(Locale.ROOT), JdbcTypeNameMapper.getTypeName(columnInformation.getTypeCode()), column.getSqlType().toLowerCase(Locale.ROOT), JdbcTypeNameMapper.getTypeName(column.getSqlTypeCode(metadata))));}}/*** @param column            模型信息* @param columnInformation 数据库信息* @return*/protected boolean validateColumnLength(Column column, ColumnInformation columnInformation, Metadata metadata, Dialect dialect) {Value value = column.getValue();String name = value.getType().getName();if (!"string".equals(name)) {return true;}
//        255 默认值忽略if (column.getLength() == 255) {return true;}
//        boolean typesMatch = column.getSqlTypeCode(metadata) == columnInformation.getTypeCode() || column.getSqlType(dialect, metadata).toLowerCase(Locale.ROOT).startsWith(columnInformation.getTypeName().toLowerCase(Locale.ROOT));
//        if (!typesMatch) {
//            return true;
//        }if (column.getSqlType(dialect, metadata).toLowerCase(Locale.ROOT).startsWith("clob")) {return true;}
//        columnInformation.getTypeName()
//        有大佬定义 columnDefinationString sqlType = column.getSqlType();if (!StringUtils.isEmpty(sqlType) && sqlType.length() > 24) {return true;}if (!(column.getLength() == columnInformation.getColumnSize())) {log.info("column {} not match length {}", column.getName(), column.getLength());return false;}return true;}public NameSpaceTablesInformation performTablesAlter(ServiceRegistry registry, Metadata metadata) {tool = (HibernateSchemaManagementTool) registry.getService(SchemaManagementTool.class);Map configurationValues = registry.getService(ConfigurationService.class).getSettings();ExecutionOptions options = new ExecutionOptions() {@Overridepublic boolean shouldManageNamespaces() {return true;}@Overridepublic Map getConfigurationValues() {return configurationValues;}@Overridepublic ExceptionHandler getExceptionHandler() {return ExceptionHandlerLoggedImpl.INSTANCE;}};NameSpaceTablesInformation tablesInformation = new NameSpaceTablesInformation(metadata.getDatabase().getJdbcEnvironment().getIdentifierHelper());jdbcContext = tool.resolveJdbcContext(options.getConfigurationValues());final DdlTransactionIsolator isolator = tool.getDdlTransactionIsolator(jdbcContext);final DatabaseInformation databaseInformation = Helper.buildDatabaseInformation(tool.getServiceRegistry(),isolator,metadata.getDatabase().getDefaultNamespace().getName());try {for (Namespace namespace : metadata.getDatabase().getNamespaces()) {if (schemaFilter.includeNamespace(namespace)) {alterTables(metadata, databaseInformation, options, jdbcContext.getDialect(), namespace);}}} finally {try {databaseInformation.cleanup();} catch (Exception e) {log.debug("Problem releasing DatabaseInformation : " + e.getMessage());}isolator.release();}return tablesInformation;}protected void alterTables(Metadata metadata, DatabaseInformation databaseInformation, ExecutionOptions options, Dialect dialect, Namespace namespace) {NameSpaceTablesInformation tables = databaseInformation.getTablesInformation(namespace);Iterator tableIter = namespace.getTables().iterator();while (tableIter.hasNext()) {Table table = (Table) tableIter.next();if (this.schemaFilter.includeTable(table) && table.isPhysicalTable()) {this.alterTable(table, tables.getTableInformation(table), metadata, options, dialect);}}}protected void alterTable(Table table, TableInformation tableInformation, Metadata metadata, ExecutionOptions options, Dialect dialect) {if (tableInformation == null) {throw new SchemaManagementException(String.format("Schema-alter: missing table [%s]", table.getQualifiedTableName().toString()));} else {Iterator selectableItr = table.getColumnIterator();while (selectableItr.hasNext()) {Selectable selectable = (Selectable) selectableItr.next();if (Column.class.isInstance(selectable)) {Column column = (Column) selectable;ColumnInformation existingColumn = tableInformation.getColumn(Identifier.toIdentifier(column.getQuotedName()));if (existingColumn == null) {throw new SchemaManagementException(String.format("Schema-alter: missing column [%s] in table [%s]", column.getName(), table.getQualifiedTableName()));}
//                    this.validateColumnType(table, column, existingColumn, metadata, dialect);if (!validateColumnLength(column, existingColumn, metadata, dialect)) {log.info("table alter:{}", table.getQualifiedTableName());boolean format = Helper.interpretFormattingEnabled(options.getConfigurationValues());Formatter formatter = format ? FormatStyle.DDL.getFormatter() : FormatStyle.NONE.getFormatter();final GenerationTarget[] targets = new GenerationTarget[]{new GenerationTargetToDatabase(tool.getDdlTransactionIsolator(jdbcContext), true)};migrateTable(table, column, tableInformation, dialect, metadata, formatter, options, targets);}}}}}protected void migrateTable(Table table, Column column, TableInformation tableInformation, Dialect dialect, Metadata metadata, Formatter formatter, ExecutionOptions options, GenerationTarget... targets) {Database database = metadata.getDatabase();AlterTable alterTable = new AlterTable(table);applySqlStrings(false, alterTable.sqlAlterStrings(dialect, metadata, tableInformation,column,database.getDefaultNamespace().getPhysicalName().getCatalog(),database.getDefaultNamespace().getPhysicalName().getSchema()),formatter,options,targets);for (int i = 0; i < targets.length; i++) {targets[i].release();}}void applySqlStrings(boolean quiet, Iterator sqlStrings, Formatter formatter, ExecutionOptions options, GenerationTarget... targets) {if (sqlStrings != null) {while (sqlStrings.hasNext()) {String sqlString = (String) sqlStrings.next();applySqlString(quiet, sqlString, formatter, options, targets);}}}private static void applySqlString(boolean quiet, String sqlString, Formatter formatter, ExecutionOptions options, GenerationTarget... targets) {if (!StringHelper.isEmpty(sqlString)) {String sqlStringFormatted = formatter.format(sqlString);GenerationTarget[] exeProcessor = targets;int excCount = targets.length;for (int i = 0; i < excCount; ++i) {GenerationTarget target = exeProcessor[i];try {target.accept(sqlStringFormatted);} catch (CommandAcceptanceException var11) {if (!quiet) {options.getExceptionHandler().handleException(var11);}}}}}
}