package cn.itcast.core.util;

import java.util.ArrayList;

import java.util.List;

public class QueryHelper {

    //from子句

    private String fromClause = "";

    //where子句

    private String whereClause = "";

    //order by子句

    private String orderByClause = "";

    private List<Object> parameters;

    //排序顺序

    public static String ORDER_BY_DESC = "DESC";//降序

    public static String ORDER_BY_ASC = "ASC";//升序

    /**

     * 构造from 子句

     * @param clazz 实体类

     * @param alias 实体类对应的别名

     */

    public QueryHelper(Class clazz, String alias){

        fromClause = "FROM " + clazz.getSimpleName() + " " + alias;

    }

    /**

     * 构造where子句

     * @param condition 查询条件语句；例如：i.title like ?

     * @param params 查询条件语句中?对应的查询条件值；例如： %标题%

     */

    public void addCondition(String condition, Object... params){

        if (whereClause.length() > 1) {//非第一个查询条件

            whereClause += " AND " + condition;

        } else {//第一个查询条件

            whereClause += " WHERE " + condition;

        }

        //设置查询条件值到查询条件值集合中

        if(parameters == null){

            parameters = new ArrayList<Object>();

        }

        if(params != null){

            for(Object param: params){

                parameters.add(param);

            }

        }

    }

    /**

     * 构造order by子句

     * @param property 排序属性，如：i.createTime

     * @param order 排序顺序，如：DESC 或者 ASC

     */

    public void addOrderByProperty(String property, String order){

        if (orderByClause.length() > 1) {//非第一个排序属性

            orderByClause += "," + property + " " + order;

        } else {//第一个排序属性

            orderByClause = " ORDER BY " + property + " " + order;

        }

    }

    //查询hql语句

    public String getQueryListHql(){

        return fromClause + whereClause + orderByClause;

    }

    //查询统计数的hql语句

    public String getQueryCountHql(){

        return "SELECT COUNT(*) " + fromClause + whereClause;

    }

    //查询hql语句中?对应的查询条件值集合

    public List<Object> getParameters(){

        return parameters;

    }

}