Ebean排序依據CASE WHEN

Question

當使用取景器Ebean，是有可能通過聲明類似下面提供了一個命令：

ORDER BY 
    CASE 
     WHEN a = 'FOO' THEN 1 
     WHEN a = 'BAR' THEN 2 
     ELSE 99 
    END 

Answer 1

這是可以做到這樣的排序。我們所要做的就是添加瞬態場，並用@Formula用適當的參數對其進行註釋。

因此，模型類應該是這樣的：

@Entity 
public class A extends Model { 

    public A(Long aId, String aA) { 
     id = aId; 
     a = aA; 
    } 

    @Id 
    public Long id; 

    @Required 
    public String a; 

    @Transient 
    @Formula(select = "(case when ${ta}.a = 'FOO' then 1 when a = 'BAR' THEN 2 else 99 end)") 
    Integer index; 

    public static Finder<Long,A> find = new Finder<Long,A>(Long.class, A.class); 
} 

這種方式，我們創建的虛擬列「指數」，我們可以通過它進行排序。

下面是示例性的測試方法：

@Test 
public void aTest() { 
    FakeApplication app = Helpers.fakeApplication(Helpers.inMemoryDatabase()); 
    Helpers.start(app); 

    A a1 = new A(1L, "BAR"); 
    A a2 = new A(2L, "XYZ"); 
    A a3 = new A(3L, "FOO"); 
    A a4 = new A(4L, "AAA"); 
    A a5 = new A(5L, "FOO"); 
    A a6 = new A(6L, "BAR"); 

    a1.save(); 
    a2.save(); 
    a3.save(); 
    a4.save(); 
    a5.save(); 
    a6.save(); 

    List<A> list = Ebean.find(A.class).orderBy("index").findList(); 
    for(A fa: list) { 
     System.out.println("fa.id:"+fa.id+" fa.a:"+fa.a); 
    } 

    System.out.println("-------------------------"); 

    List<A> list1 = A.find.orderBy("index").findList();  
    for(A fa: list1) { 
     System.out.println("fa.id:"+fa.id+" fa.a:"+fa.a); 
    } 
}