Hibernate / JPA：在更新DB Schema之前检查生成的SQL（如.NET EF迁移） [英] Hibernate/JPA: Check generated sql before updating DB Schema (like .NET EF migrations)

问题描述

所以我想学习Hibernate / JPA，我想知道是否有类似于.NET的实体框架迁移，我可以使用。

我喜欢Code First（Class - > Schema）方法，但是自动生成的sql查询可能会对数据库执行奇怪（和危险）的操作。我想验证生成的sql查询，然后决定是否要更新数据库模式。

我已经启用了 show_sql 属性。我以调试模式运行项目，以检查生成的查询，然后停止/继续执行。

有没有一种更优雅的方法可以做到这一点？我想要吗？

编辑：还有一个icremental模式更新功能吗？例如，如果我重命名模型类的字段，那么Hibernate / JPA将执行以下操作：

• 如果如果 hbm2ddl.auto = create-drop 那么它将删除表并且
重新创建它（数据丢失）。

• hbm2ddl.auto = update 然后它将添加一个
  新的colunmn与新名称。

我想要的是改变现有的表。

解决方案

是的，有一个模式生成器类。 b
$ b

org.hibernate.tool.hbm2ddl.SchemaExport

以下是我如何使用它的示例代码（请注意，这是非常高的灵感来自这里的一篇文章）

  package com.mypackage.jpa.util; 
 
 import java.io.File; 
 import java.net.URL; 
 import java.util.ArrayList; 
 import java.util.List; 
 
导入org.hibernate.cfg.Configuration; 
 import org.hibernate.tool.hbm2ddl.SchemaExport; 
 
公共类SchemaGenerator {
 
私有配置cfg; 
 
 public static void main（String [] args）throws Exception {
 
 File f = new File（。）; 
 String directory = f.getAbsoluteFile（）+/ src / main / resources / ddl / generated /; 
 
 String packageName [] = {com.mypackage.jpa，com.mypackage.jpa.legacy，com.mypackage.jpa.local，
com.mypackage .jpa.local.impl}; 
 
 SchemaGenerator gen = new SchemaGenerator（packageName）; 
 gen.generate（Dialect.MYSQL，directory）; 
 
 
 $ b @SuppressWarnings（rawtypes）
 public Sc​​hemaGenerator（String [] packagesName）抛出Exception {
 cfg = new Configuration（）; 
 cfg.setProperty（hibernate.hbm2ddl.auto，create）; （String packageName：packagesName）{
 for（Class clazz：getClasses（packageName））{
 cfg.addAnnotatedClass（clazz）; 
 
 
 
 
 
 $ b $ @SuppressWarnings（rawtypes）
 private List< Class> getClasses（String packageName）抛出异常{
 File directory = null; 
尝试{
 ClassLoader cld = getClassLoader（）; 
 URL resource = getResource（packageName，cld）; 
 directory = new File（resource.getFile（））; 
} catch（NullPointerException ex）{
 throw new ClassNotFoundException（packageName +（+ directory +）似乎不是一个有效的包）; 
} 
 return collectClasses（packageName，directory）; 
 
 
 private ClassLoader getClassLoader（）throws ClassNotFoundException {
 ClassLoader cld = Thread.currentThread（）。getContextClassLoader（）; 
 if（cld == null）{
 throw new ClassNotFoundException（Can not get class loader。）; 
} 
 return cld; 
 
 $ b $ private URL getResource（String packageName，ClassLoader cld）throws ClassNotFoundException {
 String path = packageName.replace（'。'，'/'）; 
 URL resource = cld.getResource（path）; 
 if（resource == null）{
 throw new ClassNotFoundException（No resource for+ path）; 
} 
返回资源; 
 
 
 @SuppressWarnings（rawtypes）
 private List< Class> collectClasses（String packageName，File directory）引发ClassNotFoundException {
 List< Class> classes = new ArrayList<>（）; 
 if（directory.exists（））{
 String [] files = directory.list（）; 
 for（String file：files）{
 if（file.endsWith（。class））{
 //移除.class扩展名
 classes.add（Class。 forName（packageName +'。'+ file.substring（0，file.length（） -  6）））; 
} 
} 
} else {
抛出新的ClassNotFoundException（packageName +不是有效的包）; 
} 
返回类; 
 
 $ b private void generate（dialect dialect，String directory）{
 cfg.setProperty（hibernate.dialect，dialect.getDialectClass（））; 
 SchemaExport export =新的SchemaExport（cfg）; 
 export.setDelimiter（;）; 
 export.setOutputFile（directory +ddl_+ dialect.name（）。toLowerCase（）+.sql）; 
 export.setFormat（true）; 
 export.execute（true，false，false，false）; 
 
 
 private static enum Dialect {
 ORACLE（org.hibernate.dialect.Oracle10gDialect），MYSQL（org.hibernate.dialect.MySQLDialect），HSQL 
org.hibernate.dialect.HSQLDialect），H2（org.hibernate.dialect.H2Dialect）; 
 
 private String dialectClass; 
 
私人方言（String dialectClass）{
 this.dialectClass = dialectClass; 
} 
 
 public String getDialectClass（）{
 return dialectClass; 
} 
} 
} 
  

So i am trying to learn Hibernate/JPA and i was wondering if there is something similar to .NET's Entity Framework migrations that i can use.

I like Code First (Class -> Schema) approach, but the auto generated sql queries may do strange (and dangerous) things to a database. I want to verify the generated sql query and then decide if i want to update the database schema.

I have enabled the show_sql property. I run the project in debug mode in order to check the generated query and then stop / continue the execution.

Is there a more elegant (proper?) way to do what i want?

Edit: also is there an icremental schema update feature? For instance if i rename a field of my Model's Class, then Hibernate/JPA does the following thing:

• If hbm2ddl.auto=create-drop then it will drop the table and recreate it (data loss).
• If hbm2ddl.auto=update then it will add a new colunmn with the new name.

What i want is to alter the existing table.

解决方案

Yes, there is a schema generator class.

org.hibernate.tool.hbm2ddl.SchemaExport

Here's a sample code on how I use it (note that this was very highly inspired from a post here)

    package com.mypackage.jpa.util;

    import java.io.File;
    import java.net.URL;
    import java.util.ArrayList;
    import java.util.List;

    import org.hibernate.cfg.Configuration;
    import org.hibernate.tool.hbm2ddl.SchemaExport;

    public class SchemaGenerator {

        private Configuration cfg;

        public static void main(String[] args) throws Exception {

            File f = new File(".");
            String directory = f.getAbsoluteFile() + "/src/main/resources/ddl/generated/";

            String packageName[] = { "com.mypackage.jpa", "com.mypackage.jpa.legacy", "com.mypackage.jpa.local",
                    "com.mypackage.jpa.local.impl" };

            SchemaGenerator gen = new SchemaGenerator(packageName);
            gen.generate(Dialect.MYSQL, directory);

        }

        @SuppressWarnings("rawtypes")
        public SchemaGenerator(String[] packagesName) throws Exception {
            cfg = new Configuration();
            cfg.setProperty("hibernate.hbm2ddl.auto", "create");

            for (String packageName : packagesName) {
                for (Class clazz : getClasses(packageName)) {
                    cfg.addAnnotatedClass(clazz);
                }
            }
        }

        @SuppressWarnings("rawtypes")
        private List<Class> getClasses(String packageName) throws Exception {
            File directory = null;
            try {
                ClassLoader cld = getClassLoader();
                URL resource = getResource(packageName, cld);
                directory = new File(resource.getFile());
            } catch (NullPointerException ex) {
                throw new ClassNotFoundException(packageName + " (" + directory + ") does not appear to be a valid package");
            }
            return collectClasses(packageName, directory);
        }

        private ClassLoader getClassLoader() throws ClassNotFoundException {
            ClassLoader cld = Thread.currentThread().getContextClassLoader();
            if (cld == null) {
                throw new ClassNotFoundException("Can't get class loader.");
            }
            return cld;
        }

        private URL getResource(String packageName, ClassLoader cld) throws ClassNotFoundException {
            String path = packageName.replace('.', '/');
            URL resource = cld.getResource(path);
            if (resource == null) {
                throw new ClassNotFoundException("No resource for " + path);
            }
            return resource;
        }

        @SuppressWarnings("rawtypes")
        private List<Class> collectClasses(String packageName, File directory) throws ClassNotFoundException {
            List<Class> classes = new ArrayList<>();
            if (directory.exists()) {
                String[] files = directory.list();
                for (String file : files) {
                    if (file.endsWith(".class")) {
                        // removes the .class extension
                        classes.add(Class.forName(packageName + '.' + file.substring(0, file.length() - 6)));
                    }
                }
            } else {
                throw new ClassNotFoundException(packageName + " is not a valid package");
            }
            return classes;
        }

        private void generate(Dialect dialect, String directory) {
            cfg.setProperty("hibernate.dialect", dialect.getDialectClass());
            SchemaExport export = new SchemaExport(cfg);
            export.setDelimiter(";");
            export.setOutputFile(directory + "ddl_" + dialect.name().toLowerCase() + ".sql");
            export.setFormat(true);
            export.execute(true, false, false, false);
        }

        private static enum Dialect {
            ORACLE("org.hibernate.dialect.Oracle10gDialect"), MYSQL("org.hibernate.dialect.MySQLDialect"), HSQL(
                    "org.hibernate.dialect.HSQLDialect"), H2("org.hibernate.dialect.H2Dialect");

            private String dialectClass;

            private Dialect(String dialectClass) {
                this.dialectClass = dialectClass;
            }

            public String getDialectClass() {
                return dialectClass;
            }
        }
    }

这篇关于Hibernate / JPA：在更新DB Schema之前检查生成的SQL（如.NET EF迁移）的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！