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本文主要研究下jpa的动态查询

javax.persistence.criteria

jpa从hibernate里头吸收了criteria，利用criteria结合对url查询语法的解析，也可以实现端到端的动态查询。

下面展示下springside branch 4版本中的实现。

springside branch 4

SearchFilter

/*******************************************************************************
 * Copyright (c) 2005, 2014 springside.github.io
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 *******************************************************************************/
package org.springside.modules.persistence;

import java.util.Map;
import java.util.Map.Entry;

import org.apache.commons.lang3.StringUtils;

import com.google.common.collect.Maps;

public class SearchFilter {

    public enum Operator {
        EQ, LIKE, GT, LT, GTE, LTE
    }

    public String fieldName;
    public Object value;
    public Operator operator;

    public SearchFilter(String fieldName, Operator operator, Object value) {
        this.fieldName = fieldName;
        this.value = value;
        this.operator = operator;
    }

    /**
     * searchParams中key的格式为OPERATOR_FIELDNAME
     */
    public static Map<String, SearchFilter> parse(Map<String, Object> searchParams) {
        Map<String, SearchFilter> filters = Maps.newHashMap();

        for (Entry<String, Object> entry : searchParams.entrySet()) {
            // 过滤掉空值
            String key = entry.getKey();
            Object value = entry.getValue();
            if (StringUtils.isBlank((String) value)) {
                continue;
            }

            // 拆分operator与filedAttribute
            String[] names = StringUtils.split(key, "_");
            if (names.length != 2) {
                throw new IllegalArgumentException(key + " is not a valid search filter name");
            }
            String filedName = names[1];
            Operator operator = Operator.valueOf(names[0]);

            // 创建searchFilter
            SearchFilter filter = new SearchFilter(filedName, operator, value);
            filters.put(key, filter);
        }

        return filters;
    }
}

这里定义了几种运算符EQ, LIKE, GT, LT, GTE, LTE
可以自己从mvc的controller中接收查询条件转换为SearchFilter

DynamicSpecifications

/*******************************************************************************
 * Copyright (c) 2005, 2014 springside.github.io
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 *******************************************************************************/
package org.springside.modules.persistence;

import java.util.Collection;
import java.util.List;

import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Path;
import javax.persistence.criteria.Predicate;
import javax.persistence.criteria.Root;

import org.apache.commons.lang3.StringUtils;
import org.springframework.data.jpa.domain.Specification;
import org.springside.modules.utils.Collections3;

import com.google.common.collect.Lists;

public class DynamicSpecifications {

    public static <T> Specification<T> bySearchFilter(final Collection<SearchFilter> filters, final Class<T> entityClazz) {
        return new Specification<T>() {
            @Override
            public Predicate toPredicate(Root<T> root, CriteriaQuery<?> query, CriteriaBuilder builder) {
                if (Collections3.isNotEmpty(filters)) {

                    List<Predicate> predicates = Lists.newArrayList();
                    for (SearchFilter filter : filters) {
                        // nested path translate, 如Task的名为"user.name"的filedName, 转换为Task.user.name属性
                        String[] names = StringUtils.split(filter.fieldName, ".");
                        Path expression = root.get(names[0]);
                        for (int i = 1; i < names.length; i++) {
                            expression = expression.get(names[i]);
                        }

                        // logic operator
                        switch (filter.operator) {
                        case EQ:
                            predicates.add(builder.equal(expression, filter.value));
                            break;
                        case LIKE:
                            predicates.add(builder.like(expression, "%" + filter.value + "%"));
                            break;
                        case GT:
                            predicates.add(builder.greaterThan(expression, (Comparable) filter.value));
                            break;
                        case LT:
                            predicates.add(builder.lessThan(expression, (Comparable) filter.value));
                            break;
                        case GTE:
                            predicates.add(builder.greaterThanOrEqualTo(expression, (Comparable) filter.value));
                            break;
                        case LTE:
                            predicates.add(builder.lessThanOrEqualTo(expression, (Comparable) filter.value));
                            break;
                        }
                    }

                    // 将所有条件用 and 联合起来
                    if (!predicates.isEmpty()) {
                        return builder.and(predicates.toArray(new Predicate[predicates.size()]));
                    }
                }

                return builder.conjunction();
            }
        };
    }
}

这里主要是将SearchFilter构造的查询条件转换为对应的Predicate，进而构造成jpa的Specification，来完成动态查询条件的转换。

小结

使用springside的DynamicSpecifications，再把mvc的参数映射为SearchFilter，也可以自己实现一套端到端的动态查询。

备注springside在最新版本已经删除掉这些代码，得在branch 4分支查找。

doc

• SearchFilter
• DynamicSpecifications
• 使用RSQL实现端到端的动态查询