Given that, in Objectify, an entity group is not defined by a class, but by an instance, and that you can create child entites with a parent Key that points to a nonexistant entity, how would you do that? (I'm looking for a simple example. The statements above are from Objectify documentation, and I'm confused.)
Just create a Key with an arbitrary id. A simple example:
class Foo {
#Parent Key<Par> parent;
#Id Long id;
// ...constructors, etc
}
// Create a parent key for which an entity may or may not exist, doesn't matter
Key<Par> parent = Key.create(Par.class, 123L);
Foo foo = new Foo(parent, someId);
ofy().save().entity(foo).now();
Related
I am migrating from google datastore api to objectify(i have used datastore at compute engine and migrating to 6.0a1 objectify). In previous version i used this code to query users:
KeyFactory userKeyFactory = datastore.newKeyFactory()
.addAncestors(PathElement.of("UserList", "default"))
.setKind(USER_KIND);
//...save entity
Query<Entity> query = Query.newEntityQueryBuilder()
.setKind(USER_KIND)
.setFilter(PropertyFilter.hasAncestor(datastore.newKeyFactory().setKind("UserList").newKey("default")))
.build();
QueryResults<Entity> queryResults = datastore.run(query);
List<User> result = new ArrayList<>();
queryResults.forEachRemaining(entity -> result.add(transformUser(entity)));
return result;
Now i am trying to make same query with ancestor. However objectify don't work with PathElement. So following code:
ofy().load().type(User.class).ancestor(PathElement.of("UserList", "default")).list()
fails with
java.lang.IllegalArgumentException: No class 'com.google.cloud.datastore.PathElement' was registered
at com.googlecode.objectify.impl.Registrar.getMetadataSafe(Registrar.java:115)
at com.googlecode.objectify.impl.Keys.getMetadataSafe(Keys.java:56)
at com.googlecode.objectify.impl.Keys.getMetadataSafe(Keys.java:65)
at com.googlecode.objectify.impl.Keys.rawKeyOf(Keys.java:47)
at com.googlecode.objectify.impl.Keys.anythingToRawKey(Keys.java:117)
at com.googlecode.objectify.impl.QueryImpl.setAncestor(QueryImpl.java:203)
at com.googlecode.objectify.impl.SimpleQueryImpl.ancestor(SimpleQueryImpl.java:69)
at com.googlecode.objectify.impl.LoadTypeImpl.ancestor(LoadTypeImpl.java:23)
What is proper way to use PathElement with objectify? I see i can create com.googlecode.objectify.Key and pass it as ancestor but it require class, but i don't have UserList class (it is small application, all entities related to single group).
I tried to use this code:
ofy().load().type(User.class).ancestor(datastore.newKeyFactory().setKind("UserList").newKey("default")).list()
Now it fails that User don't have field with #Parent annotation. Here is stacktrace:
com.googlecode.objectify.LoadException: Error loading Key{projectId=projectId, namespace=, path=[PathElement{kind=UserList, id=null, name=default}, PathElement{kind=User, id=1, name=null}]}: Loaded Entity has parent but com.package.model.User has no #Parent
at com.googlecode.objectify.impl.EntityMetadata.load(EntityMetadata.java:84)
at com.googlecode.objectify.impl.LoadEngine.load(LoadEngine.java:187)
at com.googlecode.objectify.impl.LoadEngine$1.nowUncached(LoadEngine.java:145)
at com.googlecode.objectify.impl.LoadEngine$1.nowUncached(LoadEngine.java:131)
at com.googlecode.objectify.util.ResultCache.now(ResultCache.java:30)
at com.googlecode.objectify.impl.Round$1.nowUncached(Round.java:66)
at com.googlecode.objectify.util.ResultCache.now(ResultCache.java:30)
at com.googlecode.objectify.impl.HybridQueryResults.lambda$load$1(HybridQueryResults.java:87)
at com.google.common.collect.Iterators$5.transform(Iterators.java:757)
at com.google.common.collect.TransformedIterator.next(TransformedIterator.java:48)
at com.google.common.collect.MultitransformedIterator.next(MultitransformedIterator.java:66)
at com.google.common.collect.Iterators$4.computeNext(Iterators.java:623)
at com.google.common.collect.AbstractIterator.tryToComputeNext(AbstractIterator.java:145)
at com.google.common.collect.AbstractIterator.hasNext(AbstractIterator.java:140)
at com.googlecode.objectify.impl.HybridQueryResults.hasNext(HybridQueryResults.java:92)
at com.googlecode.objectify.util.IteratorFirstResult.nowUncached(IteratorFirstResult.java:31)
at com.googlecode.objectify.util.ResultCache.now(ResultCache.java:30)
at com.googlecode.objectify.LoadResult.now(LoadResult.java:25)
at com.package.UserObjectifyRepository.getUserByEmail(UserObjectifyRepository.java:43)
...
Caused by: java.lang.IllegalStateException: Loaded Entity has parent but com.package.model.User has no #Parent
at com.googlecode.objectify.impl.KeyMetadata.setKey(KeyMetadata.java:142)
at com.googlecode.objectify.impl.KeyMetadata.setKey(KeyMetadata.java:122)
at com.googlecode.objectify.impl.KeyPopulator.load(KeyPopulator.java:24)
at com.googlecode.objectify.impl.translate.ClassPopulator.load(ClassPopulator.java:118)
at com.googlecode.objectify.impl.translate.ClassTranslator.loadSafe(ClassTranslator.java:109)
at com.googlecode.objectify.impl.translate.NullSafeTranslator.load(NullSafeTranslator.java:21)
at com.googlecode.objectify.impl.EntityMetadata.load(EntityMetadata.java:80)
.. 125 more
I suppose correct way to fix this is to have parent field in my User entity, something like this:
#Parent
private UserList userList;
But i haven't such entity "UserList", i need ancestor just to make query with strong consistency.
UPD: Error is gone if i adding this code:
import com.google.cloud.datastore.Key;
#Parent
private Key userList;
Is it proper way to make consistent query?
The #Parent annotation requires a key.
You just have to create a key, so it can understand that Parent/Child relationship.
I have a simple graph, with parents and children being vertices.
Parents have the relationship "isParentOf" to their children.
The vertices all have one property: the "familyName".
I want to use gremlin to match all the parents whose child's familyName is different from theirs.
Note: I cannot use the Groovy syntax of Gremlin. I must use pure Java code only.
The GremlinPipeline should look like this:
find all parents
follow the "isParentOf" relationship and get all the children
filter the children through a PipeFunction that compares the parent's "familyName" with the child's "familyName"
The problem is in the last step. How to retrieve the parent's "familyName", when this pipeline step only has access to (what is coming from the previous step, that is to say) the children?
My answer:
Accessing previous steps of a GremlinPipeline in a filter's PipeFunction is not possible. BUT it is possible if you use a PipesFunction instead (note the 's' !).
Let's look at the javadoc here:
public PipesFunction extends PipeFunction{
public AsMap getAsMap();
}
So you should setup the GremlinPipeline like this:
find all parents
name that step as "theParent"
follow the "isParentOf" relationship and get all the children
filter the children with a PipesFunction like this:
.filter(new PipesFunction<Vertex,Boolean>()
{
public Boolean compute(Vertex child) {
return parentHasDifferentFamilyName(child);
}
private Boolean parentHasDifferentFamilyName(child){
Vertex theParent = getAsMap().get("theParent");
String theParentFamilyName = theParent.getProperty("familyName");
String childFamilyName = child.getParameter("familyName");
return !(childFamilyName.equals(parentFamilyName));
}
})
Note: in the step 4, we could retrieve the "theParent" vertex thanks to the getAsMap() method, and thanks to the step 2 (that implicitly filled the "As" map).
Using Breeze, what is the simplest way to populate a GUID key when an entity is created?
I'll assume that your entity is configured such that the client is responsible for setting the Guid key for new entities. That's the default for the Guid key of an Entity Framework Code First entity; it is as if the key property were adorned with [DatabaseGenerated(DatabaseGeneratedOption.None)]
The obvious approach is to set the key after creating the entity and before adding it to the manager, e.g.:
function createFoo() {
var foo = fooType.createEntity();
foo.id(breeze.core.getUuid()); // Knockout implementation
manager.addEntity(foo);
}
This may be all you ever need.
On the other hand, you may find that you're creating new Foos in many places and for some strange reason you can't use the createFoo function. You certainly don't want to repeat that code.
You can extend the Foo entity type with id-setting behavior after which you'd be able to write:
function createFoo() {
var foo = fooType.createEntity(); // foo.id is set for you
manager.addEntity(foo);
}
There are two approaches to consider - custom constructor and type initializer; both are described in "Extending Entities"
Constructor
You can initialize the key inside a custom constructor. Breeze calls the constructor both when you create the entity and when it materializes a queried entity. Breeze will replace the initial key value when materializing.
Here's an example that assumes the Knockout model library.
function Foo() {
foo.id(breeze.core.getUuid()); // using KO
}
// one way to get the MetadataStore
var store = manager.metadataStore;
// register the ctor with the Foo type
store.registerEntityTypeCtor("Foo", Foo);
Pretty simple. The only downside is that Breeze will generate a Guid every time it makes an entity, whether creating a new one or materializing one from a query. It's wasted effort during materialization but so what? Well, I suppose that might become a performance issue although I wouldn't assume so until I had measured it.
Initializer
Suppose you measured and the repeated Guid generation is a serious problem (really?). You could set the key in a type initializer instead and only call the Guid generator when creating a new entity.
Breeze calls a type initializer after the entity has been created or materialized from query just before returning that entity to the application. Clearly you don't want to overwrite a materialized key from the database so you'll test the key value to make sure it's not real (i.e. to make sure you're fixing a created entity) before assigning it. Here's an example.
function fooInitializer(foo) {
var emptyGuid = "00000000-0000-0000-0000-000000000000";
if (foo.id() !=== emptyGuid) {
foo.id(breeze.core.getUuid());
}
}
var store = manager.metadataStore;
// register the initializer; no ctor in this example
store.registerEntityTypeCtor("Foo", function(){}, fooInitializer);
Assuming you have a Guid surrogate Key on all your entities like we have in our case, you could code a createInstance factory that does the following in a very generic approach:
function createInstance(breezeEntityManager, typeName) {
var keyProperty = breezeEntityManager.metadataStore.getEntityType(typeName, false).dataProperties.filter(function (p) {
return p.isPartOfKey;
})[0];
var config = {};
config[keyProperty.name] = breeze.core.getUuid();
return breezeEntityManager.createEntity(typeName, config);
}
This way, you won't have to create an initializer for all your entities.
I need to add multiple child objects to an existing parent Object. I am instantiating my parent object and sets it Key/Id in my UI processing layer(to which my child objects will be added).
Parent parenttoModify = new Parent();
parenttoModify.Parent_Id = 5; //this comes from some Index of a dropdown or a key column of a grid, i Have put a dummy value here for example
parenttoModify.Children.Add(child);
parenttoModify.Children.Add(child2);
DataAccess.ModifyParent(parenttoModify);
In my data access layer I have a method like :
public static bool ModifyParent(Parent parent)
{
int recordsAffected=0;
using (TestEntities testContext = new TestEntities())
{
testContext.Parents.Attach(parent);
var parentEntry = testContext.ObjectStateManager.GetObjectStateEntry(parent);
parentEntry.ChangeState(System.Data.EntityState.Modified);
recordsAffected = testContext.SaveChanges();
}
return recordsAffected > 0 ? true : false;
}
I get an error when testContext.Parent.Attach(parent) is called. It says:
Object with same key already exist.
I am not sure why is this happening since i am not adding a parent object, I am just attaching it and adding child objects within it.
Any idea where I am going wrong?
Where do you add childs? I guess you are not showing all code. When you call Attach or AddObject EF always attaches or adds all entities from object graph which are not known (tracked) to context at the moment. The exception says that some entity - probably parent - is already tracked by the context. So you have either:
Used shared context (you are creating a new instance in ModifyParent so it should not be a case)
Load parent from the context first in ModifyParent
Called Attach or AddObject on any child before attaching parent.
All these operations lead to the exception you are receiving.
I would like to know if the following is possible in JDO.
I have a 1-N relationship between a Parent and a Child class. So my classes look like
#PersistenceCapable
public class Parent {
#Persistent
private String name;
#Elements(mappedBy = "parent", dependent = "true")
private List<Children> children;
}
#PersistenceCapable
public class Child {
#Persistent
private String name;
#Persistent
private Parent parent;
}
Cascading deletes work fine. I can delete a parent and all its children will be removed from the data store.
If I query the data store for a particular child and have that query delete it, then the child is removed from the table of Child objects but its Parent's list of children will contain a null entry.
I guess this is a fairly dumb question but is there a way to get JDO to update the parent's list on deletion of a child or do I have to do this myself?
Thanks for your replies.
I recommend db4o without the DataNucleus layer. It is just getting in the way of a better performing soluton. We've done testing and found that if you use db4o directly it performs much better and uses less resources.