mybatis使用mysql的sum问题

在求和中，我们使用mysql的sum函数。

java代码

		SELECT 
		policy_id policyId,
		sum(hit_count) count
		FROM
		com_shield_policy_hit_count WHERE date > #{date} group by policy_id
	

public class ComPolicyHitCountBean implements Serializable {


    private static final long serialVersionUID = 2405225637233164110L;


    private Integer policyId;


    private Integer count = 0;


    public Integer getPolicyId() {


        return policyId;
    }


    public void setPolicyId(Integer policyId) {


        this.policyId = policyId;
    }


    public Integer getCount() {


        return count;
    }


    public void setCount(Integer count) {


        this.count = count;
    }
}

可以看到count的类型为Integer.运行程序报错

mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.executor.ExecutorException: No constructor found in com.webank.ims.operation.bean.ComPolicyHitCountBean matching [java.lang.Integer, java.math.BigDecimal]
	at org.mybatis.spring.MyBatisExceptionTranslator.translateExceptionIfPossible(MyBatisExceptionTranslator.java:75)
	at org.mybatis.spring.SqlSessionTemplate$    SqlSessionInterceptor.invoke(SqlSessionTemplate.java:371)

需要实现错误信息中的构造函数。才可以

public ComPolicyHitCountBean(Integer policyId, BigDecimal count) {
        super();
        this.policyId = policyId;
        this.count = count.intValue();
}

其实是因为mysql的sum函数返回的类型的问题。

The SUM() and AVG() functions return a DECIMAL value for exact-value arguments (integer or DECIMAL), and a DOUBLE value for approximate-value arguments (FLOAT or DOUBLE). (Before MySQL 5.0.3, SUM() and AVG() return DOUBLE for all numeric arguments.)

参考：http://bylijinnan.iteye.com/blog/1984472