javax.persistence.NoResultException：没有找到查询JPQL查询的实体

Question

@Entity
@Table(name = "ways", schema = "public", uniqueConstraints = @UniqueConstraint(columnNames = "gid"))
public class Ways implements java.io.Serializable {
private WaysId id;

public Ways() {
}

public Ways(WaysId id) {
    this.id = id;
}

@EmbeddedId
@AttributeOverrides({
        @AttributeOverride(name = "gid", column = @Column(name = "gid", unique = true)),
        @AttributeOverride(name = "classId", column = @Column(name = "class_id", nullable = false)),
        @AttributeOverride(name = "length", column = @Column(name = "length", precision = 17, scale = 17)),
        @AttributeOverride(name = "name", column = @Column(name = "name")),
        @AttributeOverride(name = "x1", column = @Column(name = "x1", precision = 17, scale = 17)),
        @AttributeOverride(name = "y1", column = @Column(name = "y1", precision = 17, scale = 17)),
        @AttributeOverride(name = "x2", column = @Column(name = "x2", precision = 17, scale = 17)),
        @AttributeOverride(name = "y2", column = @Column(name = "y2", precision = 17, scale = 17)),
        @AttributeOverride(name = "reverseCost", column = @Column(name = "reverse_cost", precision = 17, scale = 17)),
        @AttributeOverride(name = "rule", column = @Column(name = "rule")),
        @AttributeOverride(name = "toCost", column = @Column(name = "to_cost", precision = 17, scale = 17)),
        @AttributeOverride(name = "maxspeedForward", column = @Column(name = "maxspeed_forward")),
        @AttributeOverride(name = "maxspeedBackward", column = @Column(name = "maxspeed_backward")),
        @AttributeOverride(name = "osmId", column = @Column(name = "osm_id")),
        @AttributeOverride(name = "priority", column = @Column(name = "priority", precision = 17, scale = 17)),
        @AttributeOverride(name = "theGeom", column = @Column(name = "the_geom")),
        @AttributeOverride(name = "source", column = @Column(name = "source")),
        @AttributeOverride(name = "target", column = @Column(name = "target"))})
        //@AttributeOverride(name = "vitesse", column = @Column(name = "vitesse", precision = 17, scale = 17))})
public WaysId getId() {
    return this.id;
}

public void setId(WaysId id) {
    this.id = id;
}

}
@Embeddable
public class WaysId implements java.io.Serializable {

private Integer gid;
private int classId;
private Double length;
private String name;
private Double x1;
private Double y1;
private Double x2;
private Double y2;
private Double reverseCost;
private String rule;
private Double toCost;
private Integer maxspeedForward;
private Integer maxspeedBackward;
private Long osmId;
private Double priority;
private Serializable theGeom;
private Integer source;
private Integer target;
}



public double convertidTolat1(Integer id) {
    Double lat = null;
    Query query = entityManager
            .createQuery("select n.id.x1 from Ways n where n.id.gid=:id");
    query.setParameter("id", id);
    lat = (Double) query.getSingleResult();
    return lat;
}


@GET
@Path("lat/{id}")
@Produces(MediaType.APPLICATION_JSON)
public BigDecimal getlat(@PathParam(value = "id") long id) {
    BigDecimal d = iservices.getLat(id);
    return d;
}

大家好，这是我的代码，我想知道我的查询有什么问题？

Answer 1

您的查询没有问题。 Embeddables 的路径表达式在 JPA 中完全有效。你只是没有得到任何结果。 NoResultException 的 Javadoc 非常具有描述性。

在查询上执行 Query.getSingleResult() 或 TypedQuery.getSingleResult() 并且没有返回结果时由持久性提供程序抛出。此异常不会导致当前事务（如果处于活动状态）被标记为回滚。

我建议将 getSingleResult() 包装在 try-catch 块中以处理无结果的情况

Object result = null;
try {
    result = query.getSingleResult();
} catch (NoResultException e) {
    log.debug("No result forund for... ");
}

或始终使用 getResultList()，即

List results = query.getResultList();
if (results.isEmpty()) {
    return null; // handle no-results case
} else {
    return results.get(0);
}

如果您只期望一个结果，有时甚至可以进一步检查数据库完整性。

if (results.size() > 1) {
    log.warn("Found duplicated result for...");
}

Answer 2

我更喜欢这样做

public class BwJpaResultHelper {
public static Object getSingleResultOrNull(Query query){
    List results = query.getResultList();
    if (results.isEmpty()) return null;
    else if (results.size() == 1) return results.get(0);
    throw new NonUniqueResultException(results.size());
}

}

Answer 3

我认为这个会没事的。它对我有用

public Optional<UserDO> findByUserId(String userId) {
    List<UserDO> userDOList = list(namedQuery("User.findByUserId").setParameter("theUserId", userId));
    return (userDOList.isEmpty()) ? Optional.empty() : Optional.of(userDOList.get(0));
}