我使用以下POJO创建App Engine端点。
package com.incident.incidentreporter;
import java.util.Date;
import javax.jdo.annotations.IdGeneratorStrategy;
import javax.jdo.annotations.Persistent;
import javax.jdo.annotations.PrimaryKey;
import javax.persistence.Entity;
import javax.persistence.Id;
import com.google.appengine.api.datastore.Blob;
@Entity
public class Incidents {
@Id
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
private Long id;
@Persistent
private Date incidentdate;
@Persistent
private String incidentdetails;
@Persistent
private double lat;
@Persistent
private double lngtitude;
@Persistent
private String reporter;
@Persistent
private Blob incidentimage;
public Incidents() {
// TODO Auto-generated constructor stub
}
public Incidents(Long id, Date incidentdate, String incidentdetails,
double lat, double lngtitude, String reporter, Blob incidentimage) {
super();
this.id = id;
this.incidentdate = incidentdate;
this.incidentdetails = incidentdetails;
this.lat = lat;
this.lngtitude = lngtitude;
this.reporter = reporter;
this.incidentimage = incidentimage;
}
/**
* @return the incidentdate
*/
public Date getIncidentdate() {
return incidentdate;
}
/**
* @param incidentdate the incidentdate to set
*/
public void setIncidentdate(Date incidentdate) {
this.incidentdate = incidentdate;
}
/**
* @return the incidentdetails
*/
public String getIncidentdetails() {
return incidentdetails;
}
/**
* @param incidentdetails the incidentdetails to set
*/
public void setIncidentdetails(String incidentdetails) {
this.incidentdetails = incidentdetails;
}
/**
* @return the lat
*/
public double getLat() {
return lat;
}
/**
* @param lat the lat to set
*/
public void setLat(double lat) {
this.lat = lat;
}
/**
* @return the lngtitude
*/
public double getLngtitude() {
return lngtitude;
}
/**
* @param lngtitude the lngtitude to set
*/
public void setLngtitude(double lngtitude) {
this.lngtitude = lngtitude;
}
/**
* @return the reporter
*/
public String getReporter() {
return reporter;
}
/**
* @param reporter the reporter to set
*/
public void setReporter(String reporter) {
this.reporter = reporter;
}
/**
* @return the incidentimage
*/
public Blob getIncidentimage() {
return incidentimage;
}
/**
* @param incidentimage the incidentimage to set
*/
public void setIncidentimage(Blob incidentimage) {
this.incidentimage = incidentimage;
}
/**
* @return the id
*/
public Long getId() {
return id;
}
}
自动生成的端点代码如下所示。
package com.incident.incidentreporter;
import com.incident.incidentreporter.EMF;
import com.google.api.server.spi.config.Api;
import com.google.api.server.spi.config.ApiMethod;
import com.google.api.server.spi.config.ApiNamespace;
import com.google.api.server.spi.response.CollectionResponse;
import com.google.appengine.api.datastore.Cursor;
import com.google.appengine.datanucleus.query.JPACursorHelper;
import java.util.List;
import javax.annotation.Nullable;
import javax.inject.Named;
import javax.persistence.EntityExistsException;
import javax.persistence.EntityNotFoundException;
import javax.persistence.EntityManager;
import javax.persistence.Query;
@Api(name = "incidentsendpoint", namespace = @ApiNamespace(ownerDomain = "incident.com", ownerName = "incident.com", packagePath = "incidentreporter"))
public class IncidentsEndpoint {
/**
* 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 = "listIncidents")
public CollectionResponse<Incidents> listIncidents(
@Nullable @Named("cursor") String cursorString,
@Nullable @Named("limit") Integer limit) {
EntityManager mgr = null;
Cursor cursor = null;
List<Incidents> execute = null;
try {
mgr = getEntityManager();
Query query = mgr.createQuery("select from Incidents as Incidents");
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<Incidents>) 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 (Incidents obj : execute)
;
} finally {
mgr.close();
}
return CollectionResponse.<Incidents> 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 = "getIncidents")
public Incidents getIncidents(@Named("id") Long id) {
EntityManager mgr = getEntityManager();
Incidents incidents = null;
try {
incidents = mgr.find(Incidents.class, id);
} finally {
mgr.close();
}
return incidents;
}
/**
* 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 incidents the entity to be inserted.
* @return The inserted entity.
*/
@ApiMethod(name = "insertIncidents")
public Incidents insertIncidents(Incidents incidents) {
EntityManager mgr = getEntityManager();
try {
mgr.persist(incidents);
} finally {
mgr.close();
}
return incidents;
}
/**
* 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 incidents the entity to be updated.
* @return The updated entity.
*/
@ApiMethod(name = "updateIncidents")
public Incidents updateIncidents(Incidents incidents) {
EntityManager mgr = getEntityManager();
try {
if (!containsIncidents(incidents)) {
throw new EntityNotFoundException("Object does not exist");
}
mgr.persist(incidents);
} finally {
mgr.close();
}
return incidents;
}
/**
* 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.
*/
@ApiMethod(name = "removeIncidents")
public void removeIncidents(@Named("id") Long id) {
EntityManager mgr = getEntityManager();
try {
Incidents incidents = mgr.find(Incidents.class, id);
mgr.remove(incidents);
} finally {
mgr.close();
}
}
private boolean containsIncidents(Incidents incidents) {
EntityManager mgr = getEntityManager();
boolean contains = true;
try {
Incidents item = mgr.find(Incidents.class, incidents.getId());
if (item == null) {
contains = false;
}
} finally {
mgr.close();
}
return contains;
}
private static EntityManager getEntityManager() {
return EMF.get().createEntityManager();
}
}
我成功生成了客户端端点库，并将应用程序部署到Google App引擎。
我认为关键字段会自动生成。
我现在面临的问题是，如果我没有设置id字段，插入事件的代码就会失败。
我的代码中是否存在导致此问题的错误？
由于此字段是Long数据类型且必须是唯一的，是否需要添加代码才能生成它？
我正在使用Android客户端应用。
请告知。
罗纳德
答案 0 :(得分：0)
这部分
Query query = mgr.createQuery("select from Incidents as Incidents");
对我来说非常可疑。它缺少select子句中的列列表，我相信您应该查看使用列的所有后勤工作流程。这可能足以解决您的问题，但是，我相信这是您应该开始研究问题的地方。