When you change data models on the app engine to add new properties those entries without a certain property are listed with the value <missing> in the online data viewer.
What I'm wondering is how can I write a query to find those entries?
There is no direct way to query for older entities with missing attribute, but you can design data model upfront to support this. Add a version attribute to each model class. Version should have a default value, which is increased every time model class is changed and deployed. This way you will be able to query entities by version number.
There's no way to query the datastore for entities that don't have a given property. You need to iterate over all the entities and check each one - possibly by using the mapreduce API.
Or you could create a script to stick null in there for all current items that don't have that property using the low level datastore API, so then you can query on null.
I had this issue and that's how I solved it. The rough code would look like:
DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
Query query = new Query("JDOObjectType");
List<Entity> results = datastore.prepare(query).asList(FetchOptions.Builder.withLimit(9999));
for (Entity lObject : results) {
Object lProperty = lObject.getProperty("YOUR_PROPERTY");
if (lProperty == null) {
lObject.setProperty("YOUR_PROPERTY", null);
datastore.put(lProperty);
}
}
}
Related
I'm trying to create a Solr collection on SolrCloud, and I want to pass in the hosts I want the collection to exist on in a certain order, and have Solr follow that order. Solr exposes this functionality in the API with the parameter createNodeSet.shuffle, but I can't explicitly set this parameter in a SolrAdminRequest.Create instance.
Does this functionality not exist within Solrj? Can I set the value with the setProperties() method even though it's a "param"?
I'm facing this problem too, and I notice that you had opened a PR on the GitHub. I've tried several ways to achieve this goal but finally I give up by shuffling the nodes myself, before passing them to the Create request.
In Kotlin:
val nodes = listOf("node1", "node2")
val createNodeSet = nodes.shuffled().joinToString(",")
In Java:
List<String> nodes = Arrays.asList("node1", "node2");
Collections.shuffle(nodes);
String createNodeSet = String.join(",", nodes);
As current Solr now has the constructor marked as protected, only accessible via a static builder, and as I didn't want to have a new class to worry about, I figured out the following way to set the needed parameter.
This method should be usable on many of the other builder created op objects.
Create req = CollectionAdminRequest //
.createCollection(newCollection, newConfigSet, NUM_SHARDS, NUM_REPLICAS);
final SolrParams reqParams = req.getParams();
if (reqParams instanceof ModifiableSolrParams) {
((ModifiableSolrParams) reqParams).set("createNodeSet.shuffle", "false");
}
I'm currently developing a mobile application who uses a Google App Engine-hosted web service.
But i'm facing an issue. I just want to add a field in one my database's table.
App Engine doesn't use classic SQL syntax, but GQL. So i cannot use the ALTER TABLE statement. How can i do this with GQL ? I looked for a solution on the web, but there's not a lot of help.
public MyEntity() {
}
#Id
#GeneratedValue(strategy=GenerationType.IDENTITY)
private Key idStation;
private String name;
private double longitude;
private double latitude;
private java.util.Date dateRefresh = new Date(); //the field i want to add in DB
So, now when i create a "MyEntity" object, it should add the "dateRefresh" field into the database... I create my object like this:
MyEntity station = new MyEntity();
station.setName("test");
station.setLatitude(0);
station.setLongitude(0);
station.setDateRefresh(new Date("01/01/1980"));
DaoFactory.getStationDao().addStation(station);
addStation method:
#Override
public MyEntity addStation(MyEntity station) {
EntityManager em = PersistenceManager.getEntityManagerFactory().createEntityManager();
try {
em.getTransaction().begin();
em.persist(station);
em.getTransaction().commit();
} finally {
if(em.getTransaction().isActive()) em.getTransaction().rollback();
em.close();
}
return station;
}
The field "dateRefresh" is never created into my DB...
Someone to help me please ?
Thanks in advance
Just add another field to your data structure, maybe providing a default clause, and that's all. For example, if you have a UserAccount:
class UserAccount(db.Model):
user = db.UserProperty()
user_id = db.StringProperty()
you may easily add:
class UserAccount(db.Model):
user = db.UserProperty()
user_id = db.StringProperty()
extra_info = db.IntegerProperty(default=0)
timezone = db.StringProperty(default="UTC")
and let it go.
While the datastore kinda mimics tables, data is stored on a per entity basis. There is no schema or table.
All you need to do is update your model class, and new entities will be saved with the structure (fields) of the new entity.
Old entities and indexes, however, are not automatically updated. They still have the same fields as they had when they were originally written to the datastore.
There's two ways to do this. One is to make sure your code can handle situations where your new properties are missing, ie make sure no exceptions are thrown, or handle the exceptions properly when you're missing the properties.
The second way is to write a little function (usu a mapreduce function) to update every entity with appropriate or null values for your new properties.
Note that indexes are not updated unless the entity is written. So if you add a new indexed property, old entities won't show up when you query for the new property. In this case, you must use the second method and update all the entities in the datastore so that they are indexed.
I have a Silverlight 4 application with EntityFramework as data layer.
There are two entities: Customer and Products. When I get customer from a database, the related products are also read, as I added related 'Include' attribute in customer's metadata and call Include method in get query:
public IQueryable<customer> GetCustomerSetById(int customerId)
{
return this.ObjectContext.CustomerSet
.Include(o => o.Products)
.Where(o => o.Id = customerId);
}
The problem that when I change any property in customer's product I get this exception:
This EntitySet of Type
'MyApp.Web.Models.Product' does not
support the 'Edit' operation.
But everything works if I read customer products directly, e.g. not through customer entity (CustomerContext) , but via product one (ProductContext).
Also there is the IsReadOnly=true property in a product entity.
UPDATE:
I have all CUD operations and also marked all of them with related Insert, Update and Delete attributes. Otherwise it wouldn't work at all, but it works for me in some cases as I wrote above.
Any ideas?
This is the real problem with RIA+EF so we keep all our entities in one domain service because at client side it is difficult to deal with multiple entities related via navigation properties. Think for a minute it actually makes no difference and we use EF T4 template to generate all domain service operation in one class. And we generated partial methods to intercept logic of domain service methods.
It sounds like you need to make sure you have an update operation in your domain service. It will look something like this:
public void UpdateProduct(Product product)
{
ObjectContext.Products.AttachAsModified(product, ChangeSet.GetOriginal(product));
}
RIA Services EntitySet does not support 'Edit' operation
Since the aforementioned solutions do not appear to be helping try using this:
Domain Service Wizard
This wizard should look at your entity, and generate the appropriate CRUD operations.
If you then cant update your entities you have a different problem.
Have you tried moving the Include to the end?
Return this.ObjectContext.CustomerSet
.Include(o => o.Products)
.Where(o => o.Id = customerId);
Could be:
Return (from o in this.ObjectContext.CustomerSet
where o.Id = customerId
select o).Include("Products");
I am using Google App Engine's datastore and wants to retrieve an entity whose key value is written as
ID/Name
id=1
Can anyone suggest me a GQL query to view that entity in datastore admin console and also in my python program?
From your application use the get_by_id() class method of the Model:
entity = YourModel.get_by_id(1)
From Datastore viewer you should use the KEY function:
SELECT * FROM YourModel WHERE __key__ = KEY('YourModel',1)
An application can retrieve a model instance for a given Key using the get() function.
class member(db.Model):
firstName=db.StringProperty(verbose_name='First Name',required=False)
lastName=db.StringProperty(verbose_name='Last Name',required=False)
...
id = int(self.request.get('id'))
entity= member.get(db.Key.from_path('member', id))
I'm not sure how to return a specific entity in the admin console.
I have a problem with Linq and ObservableCollections in my WPF application.
Context of the problem:
I've created a very simple SQL database with two tables: User and BankAccounts.
The User Table has an one-to-many relationship with the BankAccounts Table. Next I've created Linq-to-SQL dataclasses, which worked fine ==> the assosiation between the two tables was detected as well.
Next I've created a function to retreive all Users which works fine:
DataClassesDataContext dc = new DataClassesDataContext
var query = from u in dc.Users
select u;
Now suppose I want to add a new BankAccount to each user (not very likely but still).
I could add the following code
for each(User u in query)
{
u.BankAccounts.Add(New BankAccount());
}
The above works all fine. The BankAccounts property is automaticly part of the User class, due to the assosiation in the database and Linq DataClasses.
However, in my application I first add the query results to an ObservableCollection. Hereby I could use all sorts off databinding and changenotification. This is accomplished by the following code;
ObservableCollection<User> oUsers = new ObservableCollection<User>(query);
Problem: Within the ObservableCollection I can't do anyting with the users BankAccounts property because it is now of type EntitySet<>. So I can't do the following statement anymore.
for each(User u in oUsers)
{
u.BankAccounts.Add(New BankAccount());
}
Somehow, when queryresults are added to an observablecollection It is not possible to acces the user.BankAccounts properties anymore. However, it is possible to bind the BankAccounts Property to any control, like a listbox, and it contains the correct data.
Does someone now how I can create an observableCollction (or similar collection) from wich I can access these "assosiated" properties? I'm realy looking forward for to a solution.
Thanks in advance!
Best regards,
Bas Zweeris
E: Bas.Zweeris#Capgemini.com
Keep track of the original query which will implement IQueryable, you can run any further queries you need against that.
The ObservableCollection should just be for WPF to have something to bind to - its very useful if you want to add a new collection item but not have it pushed to the database before the user has had chance to edit it.
eg.
// Create a new blank client type
var ct = new ClientType()
{
IsArchived = false,
Description = "<new client type>",
Code = "CT000",
CanLoginOnline = true
};
// Tell the data source to keep track of this object
db.ClientTypes.InsertOnSubmit(ct);
// Also add the object to the observable collection so that it can immediately be shown in the UI and editted without hitting the db
clienttypes.Add(ct);