我不知道如何使用JPQL [AND]和[OR]

如何解决我不知道如何使用JPQL [AND]和[OR]

我做了一个应用程序，它将能够搜索名字和作者的书。我使用JPQL来实现它。当我填充两个文本框（书名和作者的名字）时，它的搜索权限是正确的。但是我却填充了一个文本框。找不到搜索。 如何解决？

Book.java

@Table(name = "books")
@NamedQueries({
        @NamedQuery(name = "searchNameAndAuthor",query = "SELECT b FROM Book AS b WHERE b.book_name =:book_name and b.author=:author"),@NamedQuery(name = "searchNameAndAuthorCount",query = "SELECT count(b) FROM Book AS b WHERE b.book_name =:book_name and b.author=:author")
})
@Entity
public class Book {
    @Id
    @Column(name = "id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;

    @Column(name = "isbn_code",length = 17)
    private Integer isbn_code;

    @Column(name = "book_name",length = 30,nullable = false)
    private String book_name;

    @Column(name = "author",length = 20)
    private String author;

    @Column(name = "publisher",length = 20)
    private String publisher;

    @Column(name = "publish_date",length = 8)
    private Date publish_date;

    @Column(name = "stock",length = 4)
    private Integer stock;

search.jsp

<c:import url="/WEB-INF/views/layout/app.jsp">
    <c:param name="content">
        <c:if test="${flush != null}">
            <div id="flush_success">
                <c:out value="${flush}"></c:out>
            </div>
        </c:if>
        <h2>図書館ようこそ</h2>
        <form method="POST" action="<c:url value='/books/search/result' />">
            <label for="book_name">調べたいタイトル</label><br /> <input type="text"
                name="book_name" value="${book_name}" /> <br />
            <br />
            <label for="author">著者</label><br /> <input type="text"
                name="author" value="${author}" /> <br />
            <br />
            <button type="submit">検索</button>
        </form>
    </c:param>
</c:import>

解决方法

您还需要处理空值。一种可以检查参数是否为空的OR条件

SELECT b FROM Book AS b WHERE (:book_name IS NULL OR b.book_name =:book_name) 
                          and (:author IS NULL OR  b.author=:author)