mybatis-plus 的查询增强：多个子查询

MoreQueryWrapper.java

import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.core.toolkit.Wrappers;
import lombok.Data;

import java.util.HashMap;
import java.util.Map;

/**
 * mybatis 多查询封装。引用示例 
 * <pre>
 *   Mapper接口定义：
 *     	List<T> pageList(Page<T> page, @Param("more") MoreQueryWrapper more, @Param("column")String column, @Param("order")String order);
 *
 * 	 XML中引用 
 *     ${more.q.t2.customSqlSegment} -- 额外的查询 more.must("t2")
 *     ${more.main.customSqlSegment} -- 默认 more.getMain()
 *
 *   Java中申明
 *     MoreQueryWrapper<T> more = MoreQueryWrapper.more();
 *     more.getMain().lt("age",35);
 *     more.must("t2").eq("id",123);
 *     more.resetAliasPrefix("more"); // 默认查询对象名称是 qw ，改名时还需要这样调用
 *
 * </pre>
 *
 * 
 * Created by liao on 2022-07-07.
 */
@Data
public class MoreQueryWrapper<TM> {
	private QueryWrapper<TM> main;
	private HashMap<String, QueryWrapperWithAlias<?>> qw;
	private SafeMapGetter q;

	public MoreQueryWrapper()
	{
		this(new QueryWrapperWithAlias<TM>());
	}

	public MoreQueryWrapper(QueryWrapper<TM> main)
	{
		this.main = main;
		this.qw = new HashMap<>();
		this.q = new SafeMapGetter(this.qw);
	}

	public <T> QueryWrapperWithAlias<T> must(String key)
	{
		synchronized (this) {
			if (qw.containsKey(key)) {
				return (QueryWrapperWithAlias<T>) qw.get(key);
			}
			QueryWrapperWithAlias<T> q = new QueryWrapperWithAlias<>();
			qw.put(key, q);
			return q;
		}
	}

	/**
	 * 对子查询统一设置前缀
	 */
	public void resetAliasPrefix(String prefix)
	{
		synchronized (this) {
			String k1 = String.join(".", prefix, "q", "");
			for (String k : qw.keySet()) {
				QueryWrapperWithAlias<?> q1 = qw.get(k);
				if (q1 != null) {
					q1.setAlias(k1 + k);
				}
			}
			if (main instanceof QueryWrapperWithAlias) {
				((QueryWrapperWithAlias) main).setAlias(prefix + ".main");
			}
		}
	}


	public static <T> MoreQueryWrapper<T> more()
	{
		return new MoreQueryWrapper<T>();
	}

	public static <T> MoreQueryWrapper<T> more(QueryWrapper<T> main)
	{
		return new MoreQueryWrapper<T>(main);
	}

	public static final class SafeMapGetter extends HashMap<String, QueryWrapper<?>> {
		private final HashMap<String, QueryWrapperWithAlias<?>> qw;

		private SafeMapGetter(HashMap<String, QueryWrapperWithAlias<?>> qw)
		{
			this.qw = qw;
		}

		@Override
		public QueryWrapper<?> get(Object key)
		{
			synchronized (this) {
				if (qw != null && qw.containsKey(key)) {
					return qw.get(key);
				}
				return Wrappers.emptyWrapper();
			}
		}
	}

	@Data
	public static class QueryWrapperWithAlias<T> extends QueryWrapper<T> {
		private String alias;
		private int mark;

		public QueryWrapperWithAlias()
		{
			this(null);
		}

		public QueryWrapperWithAlias(String alias)
		{
			this.alias = alias;
		}

		@Override
		public Map<String, Object> getParamNameValuePairs()
		{
			return paramNameValuePairs;
		}

		@Override
		public String getCustomSqlSegment()
		{
			String sql = super.getCustomSqlSegment();

			// 有别名的话，修改表达式，如 more.q.t2
			// 因为 formatSqlIfNeed 方法 中直接使用了 ew 别名
			if (this.alias != null && !this.alias.isEmpty()) {
				sql = sql.replaceAll("#\\{ew\\.", String.format("#{%s.", alias));
			}

			return sql;
		}

		public QueryWrapperWithAlias<T> Mark()
		{
			this.mark++;
			return this;
		}
	}
}