Hibernate示例查询格式错误

Question

User.hbm.xml

<class name="dataAccess.User" table="USER" schema="PUBLIC" catalog="XYZ">
    <id name="userId" type="long">
        <column name="USER_ID" precision="10" scale="0" />
        <generator class="assigned" />
    </id>
    <property name="userName" type="string">
        <column name="USER_NAME" length="25" not-null="true" unique="true" />
    </property>
    <property name="emailId" type="string">
        <column name="EMAIL_ID" length="50" not-null="true" />
    </property>
    <property name="password" type="string">
        <column name="PASSWORD" length="50" not-null="true" />
    </property>
    <property name="admin" type="char">
        <column name="ADMIN" length="1" not-null="true" />
    </property>
    <property name="lastLoginTime" type="timestamp">
        <column name="LAST_LOGIN_TIME" length="23" />
    </property>

My data access function

public List findByExample(User instance) {
    log.debug("finding User instance by example");
    try {
        List results = sessionFactory.openSession()
                .createCriteria("dataAccess.User")
                .add(Example.create(instance)).list();
        System.out.println(results.size());
        log.debug("find by example successful, result size: "
                + results.size());
        return results;
    } catch (RuntimeException re) {
        log.error("find by example failed", re);
        throw re;
    }
}

I am only passing two out of the 6 attributes of the User class(username and password). But in the query it also checks for the admin field. It works fine if i put an exclude("admin") to the criteria. I cant quite figure out why this is happening.

Answer 1

I found the issue.

The default value for char is '\'. The create criteria excludes the field only if the value is found to be null. If i change it to String, it works fine.

Answer 2

Given the mapping of the admin field, we can assume that it is of type boolean. A boolean is either true of false, but never null. Why would the value of this field not be part of the example? Hibernate can't assume that false means "I want to ignore this field" and that true means "I want to find the users whose admin flag is true". You might very well look for the users whose admin flag is false.