英文:
Spring search function returning full list when nothing is searched
问题
在我的Spring应用程序中，我已经添加了一个搜索功能，用户可以在数据库中搜索姓名。它能够正常工作，除了当我搜索名称或类似名称时，但是当我不输入任何内容进行搜索时，它应该返回空，但实际上返回了完整的姓名列表。
我在逻辑中设置了如果列表为空则返回null，那么我的逻辑中有什么问题？
从测试和使用"findbyname" SQL查询来看，我认为问题在于我的SQL语句。
控制器方法如下：
@RequestMapping("search")public ModelAndView SearchBeers(@RequestParam("searchTerm") String searchTerm) {return new ModelAndView("/Searchbeers", "beerList", service.Search(searchTerm));}
服务方法如下：
public List<Beers> Search(String searchTerm) {EntityManager em = DBUtil.getEMF().createEntityManager();List<Beers> list = null;try {list = em.createNamedQuery("Beers.findByLikeName", Beers.class).setParameter("name", searchTerm).getResultList();if (list == null || list.isEmpty()) {list = null;}} finally {em.close();}return list;}
使用的SQL语句如下：
@NamedQuery(name = "Beers.findByLikeName", query = "SELECT b FROM Beers b WHERE b.name LIKE CONCAT('%', :name, '%')")
用于显示列表的JSP如下：
<c:forEach items="${beerList}" var="beer"><tr><td>${beer.id}</td><td>${beer.name}</td><td>${beer.abv}</td><td><form action="/Assignment3/beer/viewBeer"><input type="hidden" name="id" value="${beer.id}"/><input type="submit" value="<spring:message code="label.viewDetails"/>"/></form></td></tr></c:forEach>
英文:
In my spring application, I have added a search function where the user can search the database for a name, it works except when I'm searching for names or similar names, but for when the I enter nothing and search, it should return nothing but returns the full list of names.
I set the list to return null if it is null, what is the flaw in my logic?
from testing and using the findbyname SQL I think it is a flaw in my SQL state
the controller method used is
@RequestMapping("search")public ModelAndView SearchBeers(@RequestParam("searchTerm") String searchTerm) {return new ModelAndView("/Searchbeers", "beerList", service.Search(searchTerm));}
service method called is
public List<Beers> Search(String searchTerm) {EntityManager em = DBUtil.getEMF().createEntityManager();List<Beers> list = null;try {list = em.createNamedQuery("Beers.findByLikeName", Beers.class).setParameter("name", searchTerm).getResultList();if (list == null || list.isEmpty()) {list = null;}} finally {em.close();}return list;}
and the SQL statement used is
@NamedQuery(name = "Beers.findByLikeName", query = "SELECT b FROM Beers b WHERE b.name LIKE CONCAT('%',:name,'%')")
the JSP for when displaying the list is
<c:forEach items="${beerList}" var="beer"><tr><td>${beer.id}</td><td>${beer.name}</td><td>${beer.abv}</td><td><form action="/Assignment3/beer/viewBeer"><input type="hidden" name="id" value="${beer.id}"/><input type="submit" value="<spring:message code="label.viewDetails"/>"/></form></td></tr></c:forEach>
答案1
得分: 1
你有很多方法可以解决这个问题，但是问题是，当字符串为空时，你的查询是：
SELECT b from Beers b Where b.name LIKE '%%'
因此，当有一个空字符串时，你需要做另一个标记，因为LIKE '%%'会找到所有的名称。
附注：不推荐返回空值，最好是返回一个空列表。
英文:
You have many ways to solve that, but the problem is, when the String is empty your query is:
SELECT b from Beers b Where b.name LIKE '%%'
So, you need do antoher flag, when have an empty String, because ... LIKE '%%' find every name.
PD: Not a good practice return a null, is better a empty list.
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