一、背景
spring-data-mongo 实现了基于 mongodb 的 orm-mapping 能力，
通过一些简单的注解、query封装以及工具类，就可以通过对象操作来实现集合、文档的增删改查；
在 springboot 体系中，spring-data-mongo 是 mongodb java 工具库的不二之选。
二、问题产生
在一次项目问题的追踪中，发现springboot 应用启动失败，报错信息如下：
error creating bean with name 'mongotemplate' defined in class path resource [org/bootfoo/bootconfiguration.class]: bean instantiation via factory method failed; nested exception is org.springframework.beans.beaninstantiationexception: failed to instantiate [org.springframework.data.mongodb.core.mongotemplate]: factory method 'mongotemplate' threw exception; nested exception is org.springframework.dao.dataintegrityviolationexception: cannot create index for 'deviceid' in collection 't_mdevice' with keys '{ "deviceid" : 1}' and options '{ "name" : "deviceid"}'. index already defined as '{ "v" : 1 , "unique" : true , "key" : { "deviceid" : 1} , "name" : "deviceid" , "ns" : "appdb.t_mdevice"}'.; nested exception is com.mongodb.mongocommandexception: command failed with error 85: 'exception: index with name: deviceid already exists with different options' on server 127.0.0.1:27017. the full response is { "createdcollectionautomatically" : false, "numindexesbefore" : 6, "errmsg" : "exception: index with name: deviceid already exists with different options", "code" : 85, "ok" : 0.0 }
at org.springframework.beans.factory.annotation.autowiredannotationbeanpostprocessor$autowiredfieldelement.inject(autowiredannotationbeanpostprocessor.java:588)
at org.springframework.beans.factory.annotation.injectionmetadata.inject(injectionmetadata.java:88)
at org.springframework.beans.factory.annotation.autowiredannotationbeanpostprocessor.postprocesspropertyvalues(autowiredannotationbeanpostprocessor.java:366)
at org.springframework.beans.factory.support.abstractautowirecapablebeanfactory.populatebean(abstractautowirecapablebeanfactory.java:1264)
at org.springframework.beans.factory.support.abstractautowirecapablebeanfactory.docreatebean(abstractautowirecapablebeanfactory.java:553)...
caused by: org.springframework.dao.dataintegrityviolationexception: cannot create index for 'deviceid' in collection 't_mdevice' with keys '{ "deviceid" : 1}' and options '{ "name" : "deviceid"}'. index already defined as '{ "v" : 1 , "unique" : true , "key" : { "deviceid" : 1} , "name" : "deviceid" , "ns" : "appdb.t_mdevice"}'.; nested exception is com.mongodb.mongocommandexception: command failed with error 85: 'exception: index with name: deviceid already exists with different options' on server 127.0.0.1:27017. the full response is { "createdcollectionautomatically" : false, "numindexesbefore" : 6, "errmsg" : "exception: index with name: deviceid already exists with different options", "code" : 85, "ok" : 0.0 }
at org.springframework.data.mongodb.core.index.mongopersistententityindexcreator.createindex(mongopersistententityindexcreator.java:157)
at org.springframework.data.mongodb.core.index.mongopersistententityindexcreator.checkforandcreateindexes(mongopersistententityindexcreator.java:133)
at org.springframework.data.mongodb.core.index.mongopersistententityindexcreator.checkforindexes(mongopersistententityindexcreator.java:125)
at org.springframework.data.mongodb.core.index.mongopersistententityindexcreator.<init>(mongopersistententityindexcreator.java:91)
at org.springframework.data.mongodb.core.index.mongopersistententityindexcreator.<init>(mongopersistententityindexcreator.java:68)
at org.springframework.data.mongodb.core.mongotemplate.<init>(mongotemplate.java:229)
at org.bootfoo.bootconfiguration.mongotemplate(bootconfiguration.java:121)
at org.bootfoo.bootconfiguration$$enhancerbyspringcglib$$1963a75.cglib$mongotemplate$2(<generated>)
at sun.reflect.delegatingmethodaccessorimpl.invoke(unknown source)
at java.lang.reflect.method.invoke(unknown source)
at org.springframework.beans.factory.support.simpleinstantiationstrategy.instantiate(simpleinstantiationstrategy.java:162)
... 58 morecaused by: com.mongodb.mongocommandexception: command failed with error 85: 'exception: index with name: deviceid already exists with different options' on server 127.0.0.1:27017. the full response is { "createdcollectionautomatically" : false, "numindexesbefore" : 6, "errmsg" : "exception: index with name: deviceid already exists with different options", "code" : 85, "ok" : 0.0 }
at com.mongodb.connection.protocolhelper.getcommandfailureexception(protocolhelper.java:115)
at com.mongodb.connection.commandprotocol.execute(commandprotocol.java:114)
at com.mongodb.connection.defaultserver$defaultserverprotocolexecutor.execute(defaultserver.java:168)
关键信息： org.springframework.dao.dataintegrityviolationexception: cannot create index
从异常信息上看，出现的是索引冲突( command failed with error 85 )，spring-data-mongo 组件在程序启动时会实现根据注解创建索引的功能。
查看业务实体定义：
我要评论
@document(collection = "t_mdevice")
public class mdevice {
@id
private string id;
@indexed(unique=true)
private string deviceid;
deviceid 这个字段上定义了一个索引， unique=true 表示这是一个唯一索引。
我们继续 查看 mongodb中表的定义：
db.getcollection('t_mdevice').getindexes()
>>
[
{
"v" : 1,
"key" : {
"_id" : 1
},
"name" : "_id_",
"ns" : "appdb.t_mdevice"
},
{
"v" : 1,
"key" : {
"deviceid" : 1
},
"name" : "deviceid",
"ns" : "appdb.t_mdevice"
}
]
发现数据库表中同样存在一个名为 deviceid的索引，但是并非唯一索引！
三、详细分析
为了核实错误产生的原因，我们尝试通过 mongo shell去执行索引的创建，发现返回了同样的错误。
通过将数据库中的索引删除，或更正为 unique=true 之后可以解决当前的问题。
从严谨度上看，一个索引冲突导致 springboot 服务启动不了，是可以接受的。
但从灵活性来看，是否有某些方式能 禁用索引的自动创建 ，或者仅仅是打印日志呢？
尝试 google spring data mongodb disable index creation
发现 jira-datamongo-1201 在2015年就已经提出，至今未解决。
图
stackoverflow 找到许多 ，
但大多数的解答是不采用索引注解，选择其他方式对索引进行管理。
这些结果并不能令人满意。
尝试查看 spring-data-mongo 的机制，定位到 mongopersistententityindexcreator 类：
初始化方法中，会根据 mappingcontext(实体映射上下文)中已有的实体去创建索引
public mongopersistententityindexcreator(mongomappingcontext mappingcontext, mongodbfactory mongodbfactory,
indexresolver indexresolver) {
...
//根据已有实体创建
for (mongopersistententity<?> entity : mappingcontext.getpersistententities()) {
checkforindexes(entity);
}
}
在接收到mappingcontextevent时，创建对应实体的索引
public void onapplicationevent(mappingcontextevent<?, ?> event) {
if (!event.wasemittedby(mappingcontext)) {
return;
}
persistententity<?, ?> entity = event.getpersistententity();
// double check type as spring infrastructure does not consider nested generics
if (entity instanceof mongopersistententity) {
//创建单个实体索引
checkforindexes((mongopersistententity<?>) entity);
}
}
mongopersistententityindexcreator是通过mongotemplate引入的，如下：
public mongotemplate(mongodbfactory mongodbfactory, mongoconverter mongoconverter) {
assert.notnull(mongodbfactory);
this.mongodbfactory = mongodbfactory;
this.exceptiontranslator = mongodbfactory.getexceptiontranslator();
this.mongoconverter = mongoconverter == null ? getdefaultmongoconverter(mongodbfactory) : mongoconverter;
...
// we always have a mapping context in the converter, whether it's a simple one or not
mappingcontext = this.mongoconverter.getmappingcontext();
// we create indexes based on mapping events
if (null != mappingcontext && mappingcontext instanceof mongomappingcontext) {
indexcreator = new mongopersistententityindexcreator((mongomappingcontext) mappingcontext, mongodbfactory);
eventpublisher = new mongomappingeventpublisher(indexcreator);
if (mappingcontext instanceof applicationeventpublisheraware) {
((applicationeventpublisheraware) mappingcontext).setapplicationeventpublisher(eventpublisher);
}
}
}
...
//mongotemplate实现了 applicationcontextaware，当applicationcontext被实例化时被感知
public void setapplicationcontext(applicationcontext applicationcontext) throws beansexception {
prepareindexcreator(applicationcontext);
eventpublisher = applicationcontext;
if (mappingcontext instanceof applicationeventpublisheraware) {
//mappingcontext作为事件来源，向applicationcontext发布
((applicationeventpublisheraware) mappingcontext).setapplicationeventpublisher(eventpublisher);
}
resourceloader = applicationcontext;
}
...
//注入事件监听
private void prepareindexcreator(applicationcontext context) {
string[] indexcreators = context.getbeannamesfortype(mongopersistententityindexcreator.class);
for (string creator : indexcreators) {
mongopersistententityindexcreator creatorbean = context.getbean(creator, mongopersistententityindexcreator.class);
if (creatorbean.isindexcreatorfor(mappingcontext)) {
return;
}
}
if (context instanceof configurableapplicationcontext) {
//使 indexcreator 监听 applicationcontext的事件
((configurableapplicationcontext) context).addapplicationlistener(indexcreator);
}
}
由此可见， mongotemplate 在初始化时，先通过 mongoconverter 带入 mongomappingcontext，
随后完成一系列初始化，整个过程如下：
在实例化过程中，没有任何配置可以阻止索引的创建。
四、解决问题
从前面的分析中，可以发现问题关键在 indexcreator，能否提供一个自定义的实现呢，答案是可以的！
实现的要点如下
实例化bean
@bean
public mongomappingcontext mappingcontext() {
return new mongomappingcontext();
}
// 使用 mappingcontext 实例化 mongotemplate
@bean
public mongotemplate mongotemplate(mongodbfactory mongodbfactory, mongomappingcontext mappingcontext) {
mappingmongoconverter converter = new mappingmongoconverter(new defaultdbrefresolver(mongodbfactory),
mappingcontext);
converter.settypemapper(new defaultmongotypemapper(null));
mongotemplate mongotemplate = new mongotemplate(mongodbfactory, converter);
return mongotemplate;
}
自定义indexcreator
// 自定义indexcreator实现
@component
public static class customindexcreator extends mongopersistententityindexcreator {
// 构造器引用mappingcontext
public customindexcreator(mongomappingcontext mappingcontext, mongodbfactory mongodbfactory) {
super(mappingcontext, mongodbfactory);
}
public void onapplicationevent(mappingcontextevent<?, ?> event) {
persistententity<?, ?> entity = event.getpersistententity();
// 获得mongo实体类
if (entity instanceof mongopersistententity) {
system.out.println("detected mongoentity " + entity.getname());
//可实现索引处理..
}
}
}
在这里 customindexcreator继承了 mongopersistententityindexcreator ，将自动接管mappingcontextevent事件的监听。
在业务实现上可以根据需要完成索引的处理！
小结
spring-data-mongo 提供了非常大的便利性，但在灵活性支持上仍然不足。上述的方法实际上有些隐晦，在官方文档中并未提及这样的方式。
orm-mapping 框架在实现schema映射处理时需要考虑校验级别，比如 hibernate便提供了 none/create/update/validation 多种选择，毕竟这对开发者来说更加友好。
期待 spring-data-mongo 在后续的演进中能尽快完善 schema的管理功能！
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持移动技术网。
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