开启mysql后开启多个实例 mysql多个库一个实例中

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mob64ca1405664d 2023-12-26 21:21:03

文章标签 开启mysql后开启多个实例查看mysql有多个实例 spring mysql 数据库 文章分类 MySQL 数据库

使用SpringBoot + activiti6 搭建审批流项目,数据库使用的是MySQL.且我的数据库下存在多个activiti相关的数据库 schema.

org.activiti

activiti-spring-boot-starter-basic

6.0.0

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配置文件

spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver

spring.datasource.url=jdbc:mysql://localhost:3306/activiti6?useUnicode=utf8&serverTimezone=Asia/Shanghai

spring.datasource.username=root

spring.datasource.password=123456

spring.activiti.check-process-definitions=false

spring.activiti.database-schema-update=true

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因为我的数据库下已经存在了一个activiti7的数据库,所以我这次又新建了一个activiti6的数据库,然后在启动的时候没有自动创建表,而是直接进行了activiti 表的查询,并报了如下的错误

org.apache.ibatis.exceptions.PersistenceException:
### Error querying database. Cause: java.sql.SQLSyntaxErrorException: Table 'activiti6.act_ge_property' doesn't exist
### The error may exist in org/activiti/db/mapping/entity/Property.xml
### The error may involve org.activiti.engine.impl.persistence.entity.PropertyEntityImpl.selectProperty-Inline
### The error occurred while setting parameters
### SQL: select * from ACT_GE_PROPERTY where NAME_ = ?
### Cause: java.sql.SQLSyntaxErrorException: Table 'activiti6.act_ge_property' doesn't exist

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然后我就开始跟断点看源码查找问题,发现它走到了如下这段代码org.activiti.engine.impl.db.DbSqlSession(中间代码省略了一部分)

public String dbSchemaUpdate() {
String feedback = null;
boolean isUpgradeNeeded = false;
int matchingVersionIndex = -1;
if (isEngineTablePresent()) {
PropertyEntity dbVersionProperty = selectById(PropertyEntity.class, "schema.version");
....
}else {
dbSchemaCreateEngine();
}

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按预想建的是空白数据库,应该要走else的逻辑,怎么会进到if里面呢,我又继续跟了isEngineTablePresent这个方法,很简短,就是看数据库里面表是否存在

public boolean isEngineTablePresent() {
return isTablePresent("ACT_RU_EXECUTION");
}

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继续看isTablePresent方法,问题就出在下面这段代码上了,这个tables返回有内容,导致tables.next()为true

try {
tables = databaseMetaData.getTables(catalog, schema, tableName, JDBC_METADATA_TABLE_TYPES);
return tables.next();
} finally {
try {
tables.close();
} catch (Exception e) {
log.error("Error closing meta data tables", e);
}
}

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继续看,DatabaseMetaData是一个接口,断点进到了下面com.zaxxer.hikari.pool.HikariProxyDatabaseMetaData#getTables,接着调用父类的com.zaxxer.hikari.pool.ProxyDatabaseMetaData#getTables方法.

public ResultSet getTables(String catalog, String schemaPattern, String tableNamePattern, String[] types) throws SQLException {
ResultSet resultSet = this.delegate.getTables(catalog, schemaPattern, tableNamePattern, types);
Statement statement = resultSet.getStatement();
if (statement != null) {
statement = ProxyFactory.getProxyStatement(this.connection, statement);
}
return ProxyFactory.getProxyResultSet(this.connection, (ProxyStatement)statement, resultSet);
}

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this.delegate.getTables(catalog, schemaPattern, tableNamePattern, types); 这段代码进到了com.mysql.cj.jdbc.DatabaseMetaDataUsingInfoSchema这个类中.
@Override
public ResultSet getTables(String catalog, String schemaPattern, String tableNamePattern, String[] types) throws SQLException {
String db = getDatabase(catalog, schemaPattern);
db = this.pedantic ? db : StringUtils.unQuoteIdentifier(db, this.quotedId);
...
}

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继续跟getDatabase()方法.该方法实现在父类com.mysql.cj.jdbc.DatabaseMetaData中

protected String getDatabase(String catalog, String schema) {
if (this.databaseTerm.getValue() == DatabaseTerm.SCHEMA) {
return schema == null && this.nullDatabaseMeansCurrent.getValue() ? this.database : schema;
}
return catalog == null && this.nullDatabaseMeansCurrent.getValue() ? this.database : catalog;
}

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这个时候就看到了schema和catelog的都是null,然后继续跟下去的话sql就变成了如下

SELECT TABLE_SCHEMA AS TABLE_CAT, NULL AS TABLE_SCHEM, TABLE_NAME, CASE WHEN TABLE_TYPE='BASE TABLE' THEN CASE WHEN TABLE_SCHEMA = 'mysql' OR TABLE_SCHEMA = 'performance_schema' THEN 'SYSTEM TABLE' ELSE 'TABLE' END WHEN TABLE_TYPE='TEMPORARY' THEN 'LOCAL_TEMPORARY' ELSE TABLE_TYPE END AS TABLE_TYPE, TABLE_COMMENT AS REMARKS, NULL AS TYPE_CAT, NULL AS TYPE_SCHEM, NULL AS TYPE_NAME, NULL AS SELF_REFERENCING_COL_NAME, NULL AS REF_GENERATION FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME LIKE 'ACT_RU_EXECUTION' HAVING TABLE_TYPE IN ('TABLE',null,null,null,null) ORDER BY TABLE_TYPE, TABLE_SCHEMA, TABLE_NAME

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根据这个sql执行的结果可以看到我的数据库中是存在数据的

开启mysql后开启多个实例 mysql多个库一个实例中_开启mysql后开启多个实例

然后就可开始看为什么catalog为null呢,然后就继续看nullDatabaseMeansCurrent这个属性(其实跟到getDatabase()方法的时候已经进到了mysql-connector-java的类中了).

这个属性在com.mysql.cj.jdbc.DatabaseMetaData的定义为

protected RuntimeProperty nullDatabaseMeansCurrent;

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看该类的构造方法可以看到

protected DatabaseMetaData(JdbcConnection connToSet, String databaseToSet, ResultSetFactory resultSetFactory) {
this.conn = connToSet;
this.session = (NativeSession) connToSet.getSession();
this.database = databaseToSet;
this.resultSetFactory = resultSetFactory;
this.exceptionInterceptor = this.conn.getExceptionInterceptor();
this.databaseTerm = this.conn.getPropertySet().getEnumProperty(PropertyKey.databaseTerm);
this.nullDatabaseMeansCurrent = this.conn.getPropertySet().getBooleanProperty(PropertyKey.nullDatabaseMeansCurrent);
this.pedantic = this.conn.getPropertySet().getBooleanProperty(PropertyKey.pedantic).getValue();
this.tinyInt1isBit = this.conn.getPropertySet().getBooleanProperty(PropertyKey.tinyInt1isBit).getValue();
this.transformedBitIsBoolean = this.conn.getPropertySet().getBooleanProperty(PropertyKey.transformedBitIsBoolean).getValue();
this.useHostsInPrivileges = this.conn.getPropertySet().getBooleanProperty(PropertyKey.useHostsInPrivileges).getValue();
this.quotedId = this.session.getIdentifierQuoteString();
}

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在com.mysql.cj.conf.PropertyKey类中可以看到

nullDatabaseMeansCurrent("nullDatabaseMeansCurrent", "nullCatalogMeansCurrent", true), //

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然后跟到com.mysql.cj.conf.DefaultPropertySet

public DefaultPropertySet() {
for (PropertyDefinition> pdef : PropertyDefinitions.PROPERTY_KEY_TO_PROPERTY_DEFINITION.values()) {
addProperty(pdef.createRuntimeProperty());
}
}

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可以看到PropertyDefinitions.PROPERTY_KEY_TO_PROPERTY_DEFINITION

跟到com.mysql.cj.conf.PropertyDefinitions类中,果然发现了nullDatabaseMeansCurrent的定义.

new BooleanPropertyDefinition(PropertyKey.nullDatabaseMeansCurrent, DEFAULT_VALUE_FALSE, RUNTIME_MODIFIABLE,

Messages.getString("ConnectionProperties.nullCatalogMeansCurrent"), "3.1.8", CATEGORY_METADATA, Integer.MIN_VALUE),

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可以看到他的默认值为false.

然后我们在配置文件的数据库链接上加上&nullCatalogMeansCurrent=true,然后重新执行程序.发现数据库表插入正常.问题解决.

最后的配置文件:

spring.datasource.url=jdbc:mysql://localhost:3306/activiti6?useUnicode=utf8&serverTimezone=Asia/Shanghai&nullCatalogMeansCurrent=true

spring.datasource.username=root

spring.datasource.password=123456