关于QueryWrapper,实现MybatisPlus多表关联查询方式

2024-04-02 19:04:59 294人浏览独家记忆

Python 官方文档：入门教程 => 点击学习

摘要

目录QueryWrapper实现mybatisPlus多表关联查询1.dao层接口使用Select注解写sql2.service层代码示例3.反射工具类4.判空工具类Myb

QueryWrapper实现MybatisPlus多表关联查询

1.dao层接口使用Select注解写SQL

重点：@Param("ew") Wrapper参数是必须，因为${ew.customSqlSegment} 底层其实就是where 条件，所以为了保证Wrapper不为空，service层代码中的Wrapper至少需要有一个条件：1 = 1

@Override
    @Select("select a.code as code , b.name as name , b.barcode as barcode ,  a.ware_code as wareCode , c.name as wareName , a.Qty as qty , a.oprice as oprice , a.total as total , " +
            " a.id as id , a.create_by as createBy , a.create_date as createDate , a.update_by as updateBy , a.update_date as updateDate , a.status as status , a.remarks as remarks  " +
            "from sku_stock a , Goods b , warehouse c " +
            "${ew.customSqlSegment} and a.code = b.code and a.ware_code = c.code")
    IPage<SkuStock> selectPage(IPage<SkuStock> page, @Param("ew")Wrapper<SkuStock> queryWrapper);

2.service层代码示例

service父类封装的findPage方法：


    public IPage<T> findPage(T entity , Map<String , Object> search , String... args){
        long current = 1L;
        long size = 10L;
        if (EmptyUtil.isNoEmpty(ReflexUtil.getFieldValue(entity , "page")) && (long) ReflexUtil.getFieldValue(entity , "page") != 0){
            current = (long) ReflexUtil.getFieldValue(entity , "page");
        }
        if (EmptyUtil.isNoEmpty(ReflexUtil.getFieldValue(entity , "limit")) && (long) ReflexUtil.getFieldValue(entity , "limit") != 0){
            size = (long) ReflexUtil.getFieldValue(entity , "limit");
        }
 
        QueryWrapper<T> queryWrapper;
        if (EmptyUtil.isNoEmpty(search)){
            queryWrapper = new QueryWrapper<>();
            for (Map.Entry<String , Object> entry:search.entrySet()
                 ) {
                String[] key = entry.geTKEy().split(";");
                if (key.length > 1){
                    if (key[1].equals("eq")){
                        queryWrapper.eq(key[0] , entry.getValue());
                    }else if (key[1].equals("ge")){
                        queryWrapper.ge(key[0] , entry.getValue());
                    }else if (key[1].equals("lt")){
                        queryWrapper.lt(key[0] , entry.getValue());
                    }
                }else {
                    queryWrapper.like(entry.getKey() , entry.getValue());
                }
            }
        }else {
            queryWrapper = new QueryWrapper<>(entity);
        }
        queryWrapper.orderByAsc(args);
        return super.page(new Page<T>(current , size) , queryWrapper);
    }

service实现类方法：

public IPage<SkuStock> findPage(SkuStock entity, String... args) {
        Map<String , Object> search = null;
        search = new HashedMap();
        search.put("1;eq" , "1");
        if (EmptyUtil.isNoEmpty(entity.getCode())
                || EmptyUtil.isNoEmpty(entity.getWareCode())
        ){
            if (EmptyUtil.isNoEmpty(entity.getCode())){
                search.put("code" , entity.getCode());
            }
            if (EmptyUtil.isNoEmpty(entity.getWareCode())){
                search.put("ware_code" , entity.getWareCode());
            }
        }else {
            long limit = entity.getLimit();
            long page = entity.getPage();
            entity = new SkuStock();
            entity.setLimit(limit);
            entity.setPage(page);
        }
        return super.findPage(entity , search , args);
    }

3.反射工具类

package org.bluedream.comm.utils; 
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
 

public class ReflexUtil {
 
    
    public static List<Field> getObjectFields(Object obj){
        Class clazz = obj.getClass();
        List<Field> fieldList = new ArrayList<>() ;
        while (clazz != null) {//当父类为null的时候说明到达了最上层的父类(Object类).
            fieldList.addAll(Arrays.asList(clazz .getDeclaredFields()));
            clazz = clazz.getSuperclass(); //得到父类,然后赋给自己
        }
        return fieldList;
    }
 
    public static List<Field> getObjectFields(Class<?> clazz){
        List<Field> fieldList = new ArrayList<>() ;
        while (clazz != null){
            fieldList.addAll(Arrays.asList(clazz .getDeclaredFields()));
            clazz = clazz.getSuperclass(); //得到父类,然后赋给自己
        }
        return fieldList;
    }
 
    
    public static Boolean isField(String fieldName , Object entity){
        List<Field> fieldList = getObjectFields(entity);
        for (Field f1:fieldList
        ) {
            if (fieldName.equals(f1.getName()))
                return true;
        }
        return false;
    }
 
    
    public static List<Method> getObjectMethods(Object entity){
        Class<?> clazz = entity.getClass();
        List<Method> methods = new ArrayList<>();
        while (clazz != null && clazz != Object.class) {//当父类为null的时候说明到达了最上层的父类(Object类).
            methods.addAll(Arrays.asList(clazz .getDeclaredMethods()));
            clazz = clazz.getSuperclass(); //得到父类,然后赋给自己
        }
        return methods;
    }
 
    public static List<Method> getObjectMethods(Class<?> clazz){
        List<Method> methods = new ArrayList<>();
        while (clazz != null && clazz != Object.class) {//当父类为null的时候说明到达了最上层的父类(Object类).
            methods.addAll(Arrays.asList(clazz .getDeclaredMethods()));
            clazz = clazz.getSuperclass(); //得到父类,然后赋给自己
        }
        return methods;
    }
 
    
    public static Boolean isMethod(String methodName , Object entity){
        List<Method> methods = getObjectMethods(entity);
        for (Method m1:methods
        ) {
            if (methodName.equals(m1.getName()))
                return true;
        }
        return false;
    }
 
    
    public static Method getDeclaredMethod(Object obj , String methodName , Class<?>...parameterTypes) {
        for (Class<?> clazz = obj.getClass(); clazz != Object.class && clazz != null; clazz = clazz.getSuperclass()) {
            try {
                return clazz.getDeclaredMethod(methodName, parameterTypes);
            } catch (Exception e) {
                // 这里甚么都不要做！并且这里的异常必须这样写，不能抛出去。
                // 如果这里的异常打印或者往外抛，则就不会执行clazz=clazz.getSuperclass(),最后就不会进入到父类中了
            }
        }
        return null;
    }
 
    public static Object invoke(Object object, String methodName, Class<?>[] parameterTypes,
                                Object[] parameters){
        Method method = getDeclaredMethod(object, methodName, parameterTypes);
        try {
            if (method != null){
                method.setAccessible(true);
                // 调用object 的 method 所代表的方法，其方法的参数是 parameters
                return method.invoke(object, parameters);
            }
        }catch (Exception e1){
            e1.printStackTrace();
        }
        return null;
    }
 
    
 
    public static Field getDeclaredField(Object object, String fieldName) {
        Field field = null; 
        Class<?> clazz = object.getClass(); 
        for (; clazz != Object.class && clazz != null; clazz = clazz.getSuperclass()) {
            try {
                field = clazz.getDeclaredField(fieldName);
                return field;
            } catch (Exception e) {
                // 这里甚么都不要做！并且这里的异常必须这样写，不能抛出去。
                // 如果这里的异常打印或者往外抛，则就不会执行clazz = clazz.getSuperclass(),最后就不会进入到父类中了 
            }
        } 
        return null;
    }
 
    
 
    public static void setFieldValue(Object object, String fieldName, Object value) {
 
        // 根据 对象和属性名通过反射 调用上面的方法获取 Field对象
        Field field = getDeclaredField(object, fieldName);
 
        if (field != null){
            // 抑制Java对其的检查
            field.setAccessible(true);
            try {
                // 将 object 中 field 所代表的值 设置为 value
                field.set(object, value);
            } catch (IllegalArgumentException e) {
                e.printStackTrace();
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            }
        }
    }
 
    
 
    public static Object getFieldValue(Object object, String fieldName) {
        // 根据 对象和属性名通过反射 调用上面的方法获取 Field对象
        Field field = getDeclaredField(object, fieldName);
 
        if (field != null){
            // 抑制Java对其的检查
            field.setAccessible(true);
            try {
                // 获取 object 中 field 所代表的属性值
                return field.get(object);
 
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        return null;
    }  
}

4.判空工具类

package org.bluedream.comm.utils; 
import java.util.Collection;
import java.util.Map; 
public class EmptyUtil {
    //Suppress default constructor for noninstantiability
    private EmptyUtil(){
        throw new AssertionError();
    }
 
    public static boolean isEmpty(Object object){
        if (object == null){
            return true;
        }
        if (object instanceof int[]){
            return ((int[]) object).length == 0;
        }
        if (object instanceof double[]){
            return ((double[]) object).length == 0;
        }
        if (object instanceof long[]){
            return ((long[]) object).length == 0;
        }
        if (object instanceof byte[]){
            return ((byte[]) object).length == 0;
        }
        if (object instanceof short[]){
            return ((short[]) object).length == 0;
        }
        if (object instanceof float[]){
            return ((float[]) object).length == 0;
        }
        if (object instanceof char[]){
            return ((char[]) object).length == 0;
        }
        if (object instanceof Object[]){
            return ((Object[]) object).length == 0;
        }
        if (object instanceof CharSequence) {
            return ((CharSequence) object).length() == 0;
        }
        if (object instanceof Collection ){
            return ((Collection) object).isEmpty();
        }
        if (object instanceof Map){
            return ((Map) object).isEmpty();
        }
        return false;
    }
 
    public static boolean isNoEmpty(Object object){
        return !isEmpty(object);
    } 
}

MybatisPlus QueryWrapper简单用法

查询方式	说明
setSqlSelect	设置 SELECT 查询字段
where	WHERE 语句，拼接 +?WHERE 条件
and	AND 语句，拼接 +?AND 字段=值
andNew	AND 语句，拼接 +?AND (字段=值)
or	OR 语句，拼接 +?OR 字段=值
orNew	OR 语句，拼接 +?OR (字段=值)
eq	等于=
allEq	基于 map 内容等于=
ne	不等于<>
gt	大于>
ge	大于等于>=
lt	小于<
le	小于等于<=
like	模糊查询 LIKE
notLike	模糊查询 NOT LIKE
in	IN 查询
notIn	NOT IN 查询
isNull	NULL 值查询
isNotNull	IS NOT NULL
groupBy	分组 GROUP BY
having	HAVING 关键词
orderBy	排序 ORDER BY
orderAsc	ASC 排序 ORDER BY
orderDesc	DESC 排序 ORDER BY
exists	EXISTS 条件语句
notExists	NOT EXISTS 条件语句
between	BETWEEN 条件语句
notBetween	NOT BETWEEN 条件语句
addFilter	自由拼接 SQL
last	拼接在最后，例如：last(“LIMIT 1”)