您可以添加SEPARATOR为关键字。实现自己DialectResolver的关键字，并将关键字 以小写形式 添加到所得的方言中：
public class MyDialectResolver implements DialectResolver {
public Dialect resolveDialect(DialectResolutionInfo info) {
for (Database database : Database.values()) {
Dialect dialect = database.resolveDialect(info);
if (dialect != null) {
dialect.getKeywords().add("separator");
return dialect;
}
}
return null;
}
}
对于5.2.13 / 5.3.0 之前的 Hibernate版本相同：
public class MyDialectResolver extends StandardDialectResolver {
protected Dialect resolveDialectInternal(DatabaseMetaData MetaData) throws sqlException {
Dialect dialect = super.resolveDialectInternal(MetaData);
dialect.getKeywords().add("separator");
return dialect;
}
}
然后，您将不得不告诉Hibernate使用您的方言解析器。例如，在JPA中，您可以在persistence.xml中执行此操作：
<persistence>
<persistence-unit>
...
<property name="hibernate.dialect_resolvers" value="mypackage.MyDialectResolver"/>
</persistence-unit>
</persistence>
其他方言中的汇总功能也是如此。例如，在Oracle中，WITHIN缺少关键字。
还有另一种选择，它更独立于数据库（我更喜欢）。创建以下内容sqlFunction：
public class ListAggFunction implements sqlFunction {
/**
* The pattern that describes how the function is build in sql.
*
* Replacements:
* {path} - is replaced with the path of the list attribute
* {separator} - is replaced with the separator (defaults to '')
* {orderByPath} - is replaced by the path that is used for ordering the elements of the list
*/
private String pattern;
/**
* Creates a new ListAggFunction deFinition which uses the ANSI sql:2016 Syntax.
*/
public ListAggFunction() {
this("LISTAGG(DISTINCT {path}, {separator}) WITHIN GROUP(ORDER BY {orderByPath})");
}
/**
* Creates a new ListAggFunction deFinition which uses a database specific Syntax.
*
* @param pattern The pattern that describes how the function is build in sql.
*/
public ListAggFunction(String pattern) {
this.pattern = pattern;
}
public Type getReturnType(Type firstArgumentType, Mapping mapping) throws QueryException {
return StringType.INSTANCE;
}
public boolean hasArguments() {
return true;
}
public boolean hasParenthesesIfNoArguments() {
return true;
}
public String render(Type firstArgumentType, List arguments,
SessionFactoryImplementor factory) throws QueryException {
if (arguments.isEmpty() || arguments.size() > 3) {
throw new IllegalArgumentException(
"Expected arguments for 'listagg': path [, separator [, order by path]]");
}
String path = (String) arguments.get(0);
String separator = arguments.size() < 2 ? "''" : (String) arguments.get(1);
String orderByPath = arguments.size() <= 2 ? path : (String) arguments.get(2);
return StringUtils.replaceEach(this.pattern, new String[] { "{path}", "{separator}", "{orderByPath}" },
new String[] { path, separator, orderByPath });
}
}
您可以使用与上面的关键字相同的方式在DialectResolver中注册此功能：
if ("MysqL".equals(info.getDatabaseName()) || "H2".equals(info.getDatabaseName())) {
dialect.getFunctions().put("listagg", new ListAggFunction("GROUP_CONCAT(DISTINCT {path} ORDER BY {orderByPath} SEPARATOR {separator})"));
} else {
dialect.getFunctions().put("listagg", new ListAggFunction());
}
现在，您可以在JPQL / HQL / Criteria查询中使用此功能，而无需考虑方言的语法：
SELECT e.group, listagg(e.stringProperty, ', ') FROM Entity e GROUP BY e.group
602392714
清零编程群