mybatis generator 如何使用提供的example类，完成 a = 1 and (b = 2 or c =2)的逻辑

对于这个问题，我可以给出以下回答：

使用Mybatis Generator提供的Example类可以实现查询条件拼装，其中and、or的条件可以通过Example类自带的Criteria对象实现，具体的代码实现如下：

Example example = new Example(MyTable.class);
Criteria criteria = example.createCriteria();
criteria.andEqualTo("a", 1).andEqualTo("b", 2).orEqualTo("c", 2);

在上面的代码中，我们首先创建了一个MyTable类的Example对象，然后通过createCriteria()方法创建了一个Criteria对象，并且通过andEqualTo()和orEqualTo()方法实现了查询条件的拼装。最终的查询条件为：a=1 and (b=2 or c=2)。

通过这种方式，我们可以使用Mybatis Generator提供的Example类很方便地实现复杂的查询条件拼装。

相关问题

mybatis generator 如何使用提供的example类，完成 a = 1 and (b = 2 or b =3)的逻辑

答：可以通过 Example 类的 createCriteria() 方法创建一个 Criteria 对象，然后调用 Criteria 的 andEqualTo()、orEqualTo() 方法来实现 a = 1 and (b = 2 or b = 3) 的逻辑。示例代码如下：

Example example = new Example(MyEntity.class);
Criteria criteria = example.createCriteria();
criteria.andEqualTo("a", 1);
criteria.andOrEqualTo("b", 2, 3);

List<MyEntity> entities = myMapper.selectByExample(example);

其中，"a" 和 "b" 是 MyEntity 类的属性名。

mybatis雪花算法生成id

MyBatis并没有内置雪花算法生成ID的方法，但可以通过自定义插件实现。以下是一个简单的示例：

1. 定义SnowflakeIdGenerator类，实现雪花算法生成ID的逻辑：

public class SnowflakeIdGenerator {
    private long workerId;
    private long datacenterId;
    private long sequence = 0L;
    private long twepoch = 1288834974657L;
    private long workerIdBits = 5L;
    private long datacenterIdBits = 5L;
    private long maxWorkerId = -1L ^ (-1L << workerIdBits);
    private long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
    private long sequenceBits = 12L;
    private long workerIdShift = sequenceBits;
    private long datacenterIdShift = sequenceBits + workerIdBits;
    private long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
    private long sequenceMask = -1L ^ (-1L << sequenceBits);
    private long lastTimestamp = -1L;

    public SnowflakeIdGenerator(long workerId, long datacenterId) {
        if (workerId > maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
        }
        if (datacenterId > maxDatacenterId || datacenterId < 0) {
            throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
        }
        this.workerId = workerId;
        this.datacenterId = datacenterId;
    }

    public synchronized long nextId() {
        long timestamp = timeGen();

        if (timestamp < lastTimestamp) {
            throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
        }

        if (lastTimestamp == timestamp) {
            sequence = (sequence + 1) & sequenceMask;
            if (sequence == 0) {
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            sequence = 0L;
        }

        lastTimestamp = timestamp;

        return ((timestamp - twepoch) << timestampLeftShift) |
                (datacenterId << datacenterIdShift) |
                (workerId << workerIdShift) |
                sequence;
    }

    protected long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }

    protected long timeGen() {
        return System.currentTimeMillis();
    }
}

2. 实现自定义插件，使用SnowflakeIdGenerator生成ID并注入到参数中：

@Intercepts({@Signature(type = StatementHandler.class, method = "update", args = {Statement.class})})
public class SnowflakeIdInterceptor implements Interceptor {
    private SnowflakeIdGenerator idGenerator = new SnowflakeIdGenerator(0L, 0L);

    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        StatementHandler statementHandler = (StatementHandler) invocation.getTarget();
        MetaObject metaObject = SystemMetaObject.forObject(statementHandler);
        MappedStatement mappedStatement = (MappedStatement) metaObject.getValue("delegate.mappedStatement");
        String idParamName = mappedStatement.getId() + ".id";
        ParameterHandler parameterHandler = (ParameterHandler) metaObject.getValue("delegate.parameterHandler");
        Object parameterObject = parameterHandler.getParameterObject();
        if (parameterObject instanceof Map) {
            ((Map) parameterObject).put(idParamName, idGenerator.nextId());
        } else {
            Field idField = parameterObject.getClass().getDeclaredField("id");
            idField.setAccessible(true);
            idField.set(parameterObject, idGenerator.nextId());
        }
        return invocation.proceed();
    }

    @Override
    public Object plugin(Object target) {
        return Plugin.wrap(target, this);
    }

    @Override
    public void setProperties(Properties properties) {
        String workerId = properties.getProperty("workerId");
        String datacenterId = properties.getProperty("datacenterId");
        if (workerId != null && datacenterId != null) {
            idGenerator = new SnowflakeIdGenerator(Long.parseLong(workerId), Long.parseLong(datacenterId));
        }
    }
}

3. 在MyBatis配置文件中注册插件：

<plugins>
    <plugin interceptor="com.example.SnowflakeIdInterceptor">
        <property name="workerId" value="0"/>
        <property name="datacenterId" value="0"/>
    </plugin>
</plugins>

其中，workerId和datacenterId为雪花算法中的参数。可以根据实际情况进行配置。