Question

我正在尝试使用标准JPA方法在Spring应用程序中实现分页。这是一个非常简单的例子：

TypedQuery<Department> depsQuery = em.createQuery("select d from Department d", Department.class);
depsQuery.setFirstResult(20);
depsQuery.setMaxResults(10);
depsQuery.getResultList();

此查询应在Informix中生成类似select skip 20 first 10的内容。但是，它产生了这个：

select first 30 department0_.id as ... from DEPARTMENT department0_

我在<driver-class>com.informix.jdbc.IfxDriver</driver-class>的JBoss standalone.xml和<property name="hibernate.dialect" value="org.hibernate.dialect.InformixDialect" />文件中persistence.xml。如何让Hibernate / JDBC生成正确的查询？

Answer 1

“org.hibernate.dialect.InformixDialect”不支持限制。这是该课程的片段：

public boolean supportsLimitOffset() {
        return false;
    }

    public String getLimitString(String querySelect, int offset, int limit) {
        if ( offset > 0 ) {
            throw new UnsupportedOperationException( "query result offset is not supported" );
        }
        return new StringBuffer( querySelect.length() + 8 )
                .append( querySelect )
                .insert( querySelect.toLowerCase().indexOf( "select" ) + 6, " first " + limit )
                .toString();
    }

您可以扩展此类以创建自定义方言。然后覆盖上述两种方法。

public boolean supportsLimitOffset() {
    return true;
}

public String getLimitString(String querySelect, int offset, int limit) {
    return new StringBuffer( querySelect.length() + 8 )
            .append( querySelect )
            .insert( querySelect.toLowerCase().indexOf( "select" ) + 6," skip " + offset + " first " + limit).toString();
}

Answer 2

我遇到了同样的问题，上面的答案对我没有帮助。仅覆盖getLimitString方法无效。我也必须覆盖LimitHandler并打开一些boolean-Flags。

import org.hibernate.dialect.pagination.AbstractLimitHandler;
import org.hibernate.dialect.pagination.LimitHandler;
import org.hibernate.engine.spi.RowSelection;

public class TestDialect extends org.hibernate.dialect.InformixDialect {

    private static final LimitHandler LIMIT_HANDLER = new AbstractLimitHandler() {
        @Override
        public String processSql(String sql, RowSelection selection) {
            return getMyLimitString(sql, selection.getFirstRow(), selection.getMaxRows());
        }

        @Override
        public boolean supportsLimit() {
            return true;
        }

        @Override
        public boolean bindLimitParametersFirst() {
            return true; // must do, otherwise there will be an exception cause of preparedStatments
        }
    };

    //
    ////
    //

    public TestDialect() {
        super();
    }


    @Override
    public LimitHandler getLimitHandler() {
        return LIMIT_HANDLER;
    }

    @Override
    public String getLimitString(String querySelect, int offset, int limit) {       
        return getMyLimitString(querySelect, offset, limit);
    }

    public static String getMyLimitString(String querySelect, int offset, int limit) {
        /* SQL Syntax:
         * SELECT FIRST <limit> ...
         * SELECT SKIP <offset> FIRST <limit> ...
         */


        System.out.println("TestDialect.getMyLimitString()");

        if (offset < 0 || limit < 0) {
            throw new IllegalArgumentException("Cannot perform limit query with negative limit and/or offset value(s)");
        }

        StringBuffer limitQuery = new StringBuffer(querySelect.length() + 10);
        limitQuery.append(querySelect);
        int indexOfEndOfSelect = querySelect.toLowerCase().indexOf("select") + 6;

        if (offset == 0) {
            limitQuery.insert(indexOfEndOfSelect, " first ?"  );
        } else {
            limitQuery.insert(indexOfEndOfSelect, " skip ?" +   " first ?"  );
        }

        return limitQuery.toString();
    }

    @Override
    public boolean supportsLimit() {
        return true;
    }
}

Hibernate / JDBC为Informix数据库生成错误的SQL

2 个答案: