使用 Google App Engine，我为一个Client类创建了一个端点。当我使用简单的 GET 语句访问它时，它会出错。即使我只插入了简单的数据，也会发生这种情况。
我在最后放了一些我的类的骨架代码。private List<Assessment> assessment我猜我需要对类中的行做一些花哨的注释Client，但我不知道该怎么做。
有谁知道如何解决这个问题，如果可能的话，我想知道为什么这个错误与设置有关，因为评估字段中没有数据。
插入的数据
{
"firstName" : "Jon",
"lastName" : "Doe"
}
插入后，我执行这个简单的语句来选择所有firstName和lastName字段。
GET http://localhost:8888/_ah/api/clientendpoint/v1/client?fields=items(firstName%2Cid%2ClastName)
这是我返回错误的地方
错误
com.google.appengine.repackaged.org.codehaus.jackson.map.JsonMappingException：您刚刚尝试访问字段“assessment”，但在您分离对象时未分离此字段。要么不要访问此字段，要么在分离对象时将其分离。（通过引用链：com.google.api.server.spi.response.CollectionResponse[\"items\"]->com.google.appengine.datanucleus.query.StreamingQueryResult[0]->com.my.app.client .客户[\"评估\"])
更新：我通过 Eclipse Google API 插件生成了端点。我把它放在最后，它对应于 GET 语句。
我进一步追查了一下，这可能只是我对如何创建返回的对象缺乏了解。
错误似乎在
com.my.app.client.Client.jdoGetassessment(Client.java) com.my.app.client.Client.getAssessment(Client.java:247)
但jdoGetAssessment()在我的代码中不存在，所以我猜这是在 Google App Engine 中生成的。getAssessment()由定义。
public List<Assessment> getAssessment() {
return assessment;
}
这似乎触发了错误消息，但我仍然不明白为什么会在没有数据的情况下触发它。
客户
@Entity
public class Client {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Key id;
private String firstName;
private String lastName;
@ElementCollection
private List<Assessment> assessment;
public Key getId() {
return id;
}
public void setId(Key id) {
this.id = id;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public List<Assessment> getAssessment() {
return assessment;
}
public void setAssessment(List<Assessment> assessment) {
this.assessment = assessment;
}
}
评估
@Embeddable
public class Assessment {
private Date date;
public Date getDate() {
return date;
}
public void setDate(Date date) {
this.date = date;
}
}
生成的ClientEndpoint.java
@Api(name = "clientendpoint", namespace = @ApiNamespace(ownerDomain = "myapp.com", ownerName = "myapp.com", packagePath = "mypackage.client"))
public class ClientEndpoint {
/**
* This method lists all the entities inserted in datastore.
* It uses HTTP GET method and paging support.
*`
* @return A CollectionResponse class containing the list of all entities
* persisted and a cursor to the next page.
*/
@SuppressWarnings({ "unchecked", "unused" })
@ApiMethod(name = "listClient")
public CollectionResponse<Client> listClient(
@Nullable @Named("cursor") String cursorString,
@Nullable @Named("limit") Integer limit) {
EntityManager mgr = null;
Cursor cursor = null;
List<Client> execute = null;
try {
mgr = getEntityManager();
Query query = mgr.createQuery("select from Client as Client");
if (cursorString != null && cursorString != "") {
cursor = Cursor.fromWebSafeString(cursorString);
query.setHint(JPACursorHelper.CURSOR_HINT, cursor);
}
if (limit != null) {
query.setFirstResult(0);
query.setMaxResults(limit);
}
execute = (List<Client>) query.getResultList();
cursor = JPACursorHelper.getCursor(execute);
if (cursor != null)
cursorString = cursor.toWebSafeString();
// Tight loop for fetching all entities from datastore and accomodate
// for lazy fetch.
for (Client obj : execute)
;
} finally {
mgr.close();
}
return CollectionResponse.<Client> builder().setItems(execute)
.setNextPageToken(cursorString).build();
}
/**
* This method gets the entity having primary key id. It uses HTTP GET method.
*
* @param id the primary key of the java bean.
* @return The entity with primary key id.
*/
@ApiMethod(name = "getClient")
public Client getClient(@Named("id") Long id) {
EntityManager mgr = getEntityManager();
Client client = null;
try {
client = mgr.find(Client.class, id);
} finally {
mgr.close();
}
return client;
}
/**
* This inserts a new entity into App Engine datastore. If the entity already
* exists in the datastore, an exception is thrown.
* It uses HTTP POST method.
*
* @param client the entity to be inserted.
* @return The inserted entity.
*/
@ApiMethod(name = "insertClient")
public Client insertClient(Client client) {
EntityManager mgr = getEntityManager();
try {
if (containsClient(client)) {
throw new EntityExistsException("Object already exists");
}
mgr.persist(client);
} finally {
mgr.close();
}
return client;
}
/**
* This method is used for updating an existing entity. If the entity does not
* exist in the datastore, an exception is thrown.
* It uses HTTP PUT method.
*
* @param client the entity to be updated.
* @return The updated entity.
*/
@ApiMethod(name = "updateClient")
public Client updateClient(Client client) {
EntityManager mgr = getEntityManager();
try {
if (!containsClient(client)) {
throw new EntityNotFoundException("Object does not exist");
}
mgr.persist(client);
} finally {
mgr.close();
}
return client;
}
/**
* This method removes the entity with primary key id.
* It uses HTTP DELETE method.
*
* @param id the primary key of the entity to be deleted.
* @return The deleted entity.
*/
@ApiMethod(name = "removeClient")
public Client removeClient(@Named("id") Long id) {
EntityManager mgr = getEntityManager();
Client client = null;
try {
client = mgr.find(Client.class, id);
mgr.remove(client);
} finally {
mgr.close();
}
return client;
}
private boolean containsClient(Client client) {
if (client.getId() == null)
return false;
EntityManager mgr = getEntityManager();
boolean contains = true;
try {
Client item = mgr.find(Client.class, client.getId());
if (item == null) {
contains = false;
}
} finally {
mgr.close();
}
return contains;
}
private static EntityManager getEntityManager() {
return EMF.get().createEntityManager();
}
}