如何对MySQL进行动态查询

Question

I used Spring MVC , how can I made a dynamic query for Mysql ? I have in my controller something like that: public String getNewsByDateAndAuthor(Model model, HttpServletRequest request) {}

How can I used all my parameters from URL with request.getParameterMap() , and my map are <String, List<String>> to create a dynamic query with that?

For example, if I have 3 parameters I want to generate one query like that:

SELECT * FROM news WHERE parameter = IN(val1, val2...) AND parameter2 = IN(val1, val2...) AND parameter3 = IN(val1, val2...)

or something like that is I have just one parameter;

SELECT * FROM news WHERE parameter = IN(val1, val2...)

If anyone know please show me how I can do that.

I want some code like that:

public String getQuery(Map<String,List<String>> parameters){
        List<String> author = new ArrayList<>();
        List<String> startDate = new ArrayList<>();
        List<String> endDate = new ArrayList<>();
        List<String> categories = new ArrayList<>();
        List<String> about = new ArrayList<>();
        List<String> soureID = new ArrayList<>();

        if (!parameters.get("author").isEmpty())
            for (int i = 0; i < parameters.get("author").size(); i++) {
                author.add(parameters.get("author").get(i));
            }

        if (!parameters.get("startDate").isEmpty())
            for (int i = 0; i < parameters.get("startDate").size(); i++) {
                startDate.add(parameters.get("startDate").get(i));
            }

        if (!parameters.get("endDate").isEmpty())
            for (int i = 0; i < parameters.get("endDate").size(); i++) {
                endDate.add(parameters.get("endDate").get(i));
            }

        if (!parameters.get("categories").isEmpty())
            for (int i = 0; i < parameters.get("categories").size(); i++) {
                categories.add(parameters.get("categories").get(i));
            }

        if (!parameters.get("about").isEmpty())
            for (int i = 0; i < parameters.get("about").size(); i++) {
                about.add(parameters.get("about").get(i));
            }

        if (!parameters.get("soureID").isEmpty())
            for (int i = 0; i < parameters.get("soureID").size(); i++) {
                soureID.add(parameters.get("soureID").get(i));
            }

        StringBuilder queryBuilder = new StringBuilder();
        queryBuilder.append("SELECT * FROM news WHERE");

        if (!author.isEmpty()) {
            String authors = author.toString();
            authors.replace(" ", " , ");
            queryBuilder.append(" author = IN ( " + authors + " ) AND");
        }
        if (!startDate.isEmpty()) {
            String startDates = startDate.toString();
            startDates.replace(" ", " , ");
            queryBuilder.append(" author = IN ( " + startDates + " ) AND");
        }
        if (!endDate.isEmpty()) {
            String endDates = endDate.toString();
            endDates.replace(" ", " , ");
            queryBuilder.append(" author = IN ( " + endDates + " ) AND");
        }
        if (!categories.isEmpty()) {
            String categoriesR = categories.toString();
            categoriesR.replace(" ", " , ");
            queryBuilder.append(" author = IN ( " + categoriesR + " ) AND");
        }
        if (!about.isEmpty()) {
            String abouts = about.toString();
            abouts.replace(" ", " , ");
            queryBuilder.append(" author = IN ( " + abouts + " ) AND");
        }
        if (!soureID.isEmpty()) {
            String sourceIDs = soureID.toString();
            sourceIDs.replace(" ", " , ");
            queryBuilder.append(" author = IN ( " + sourceIDs + " ) AND");
        }

        queryBuilder.delete(queryBuilder.length() - 3, queryBuilder.length());

        String query = queryBuilder.toString();

        return query;
}

Answer 1

You don't want a method like that, you don't want to use String concats to create a dynamic query. You want to use the Criteria API for that.

Something like the following

CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<News> cq = cb.createQuery(News.class);
Root<News> news = cq.from(News.class);

if (!parameters.get("author").isEmpty()) {
    cq.where(cb.in(news.get("author"), parameters.get("author"));
}

TypedQuery<News> query = em.createQuery(cq);
return query.getResultList();

As you have multiple results you probably first want to create a list of Predicates and then apply them using cq.where(cb.and(predicates.toArray(new Predicate[predicates.size()]); .

CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<News> cq = cb.createQuery(News.class);
Root<News> news = cq.from(News.class);
List<Predicate> predicates = new ArrayList<Predicate>();

if (!parameters.get("author").isEmpty()) {
    predicates.add(cb.in(news.get("author"), parameters.get("author")));
}

// Other params here.

cq.where(cb.and(predicates.toArray(new Predicate[predicates.size()]));
TypedQuery<News> query = em.createQuery(cq);
return query.getResultList();