For example I load an entity in the following way:
Movie m = session.load(Movie.class, id, 0); // load properties but not relationships
m.getActors(); // empty since depth was 0
A bit later in another method:
// Do I need to load it?
if (needsLoad(m) {
m = session.load(Movie.class, m.getId(), 1);
}
for (Actor a : m.getActors()) {
// ...
}
The only solution I've found is to load it every time.
Is there a better approach?
There is no API for accessing the session cache.
As a result it is not possible to get information about how deep the object graph got loaded.
I wonder how you get in the situation to need this.
The standard approach would be: load data from the database with the "right" depth, manipulate the data and save it back.
All within one transaction.
Related
I am currently working with parse in react native.
I have a query that fetches data from a collection which has a property with relation to other collection.
Now i want to fetch all these relational data in a single call rather then calling each relation separately.
Currently i get one collection then get its relational data separately in a new call.
const data1 = await result
.get("data1")
.query()
.descending("createdAt")
.find();
const data2 = data1.relation("test");
const data3 = await data2.query().find();
Now i want to fetch the relational data along with the data1 in the very first call.
I would like to know is it even possible in parse.
If yes how?
I have been trying to fetch relational data all day but no success.
Any help would really be appreciated.
I hope you're fine :)
Using relations, you will need to fetch the data with more than a single call.
Why is it necessary?
It is required because the relation type creates a new collection on the database to store the relational data.
Please, take a look at the code below:
query.find().then(results => {
for (var i = results.length - 1; i >= 0; i--) {
let object = results[i];
object.relation("data1").query().each(function(relatedObject) {
console.log(relatedObject);
/* .... */
});
}
}).catch(console.error());
Is there another option to receive the data in a single call?
Yes, there is! To configure this option, you will need to use the pointer or array type, then you will be able to use include() method and get the column value, please read more about it below:
https://docs.parseplatform.org/js/guide/#one-to-many
I am looking for a query (lucene, fts-alfresco or ...) to return all the document which have a specific child association (that is not null).
Some context:
Documents of type abc:document have a child-association abc:linkedDocument.
Not all document have an other document linked to them, some have none some have one or multiple.
I need a fast and easy way to get an overview of all the documents that do have at least one document linked to them.
Currently I have a webscript that does what I need, but prefer not to have tons of webscripts which are not business related.
code:
SearchParameters sp = new SearchParameters();
String query = "TYPE:\"abc:document\"";
StoreRef store = StoreRef.STORE_REF_WORKSPACE_SPACESSTORE;
sp.addStore(store);
sp.setLanguage(SearchService.LANGUAGE_FTS_ALFRESCO);
sp.setQuery(query);
ResultSet rs = services.getSearchService().query(sp);
List<NodeRef> nodeRefs = rs.getNodeRefs();
for (NodeRef ref : nodeRefs) {
List<ChildAssociationRef> refs = services.getNodeService().getChildAssocs(ref);
for(ChildAssociationRef chref : refs){
if(chref.getQName().equals(AbcModel.ASSOC_LINKED_DOC)){
logger.debug("Document with linked doc: {}", ref);
break;
}
}
}
Associations aren't query-able so you'll have to do what you are doing, which is essentially checking every node in a result set for the presence of a desired association.
The only improvement I can suggest is that you can ask for the child associations of a specific type which would prevent you from having to check the type of every child association, see How to get all Child associations with a specific Association Type Alfresco (Java)
I learned that is this how to access a model from other controller,
var book = Alloy.Models.instance('book');
And this is how to access a property of a model,
var name = book.get('name');
However in the console,the name logs [INFO] : { } , meaning this doesn't get its property value, and ofcourse the model has already a data saved on it. Thanks for your help!
You may have to fetch the collection first:
var books = Alloy.Collections.book;
books.fetch();
This will load all the models from the collection so you can use them.
although the above works, there are a few addtional points here.
the call is asynchronous in most cases so you should be getting the model in a callback which is not presented in the code above.
I dont know if fetching the collection everytime you want a model is the correct approach either? If the collection already exists you just need to get the model from the collection just using the id.
depending on the exact use case, you might just want to pass the model as a parameter from one controller to the next
Starting with a List of entities and needing all dependent entities through an association, is there a way to use the corresponding navigation-propertiy to load all child-entities with one db-round-trip? Ie. generate a single WHERE fkId IN (...) statement via navigation property?
More details
I've found these ways to load the children:
Keep the set of parent-entities as IQueriable<T>
Not good since the db will have to find the main set every time and join to get the requested data.
Put the parent-objects into an array or list, then get related data through navigation properties.
var children = parentArray.Select(p => p.Children).Distinct()
This is slow since it will generate a select for every main-entity.
Creates duplicate objects since each set of children is created independetly.
Put the foreign keys from the main entities into an array then filter the entire dependent-ObjectSet
var foreignKeyIds = parentArray.Select(p => p.Id).ToArray();
var children = Children.Where(d => foreignKeyIds.Contains(d.Id))
Linq then generates the desired "WHERE foreignKeyId IN (...)"-clause.
This is fast but only possible for 1:*-relations since linking-tables are mapped away.
Removes the readablity advantage of EF by using Ids after all
The navigation-properties of type EntityCollection<T> are not populated
Eager loading though the .Include()-methods, included for completeness (asking for lazy-loading)
Alledgedly joins everything included together and returns one giant flat result.
Have to decide up front which data to use
It there some way to get the simplicity of 2 with the performance of 3?
You could attach the parent object to your context and get the children when needed.
foreach (T parent in parents) {
_context.Attach(parent);
}
var children = parents.Select(p => p.Children);
Edit: for attaching multiple, just iterate.
I think finding a good answer is not possible or at least not worth the trouble. Instead a micro ORM like Dapper give the big benefit of removing the need to map between sql-columns and object-properties and does it without the need to create a model first. Also one simply writes the desired sql instead of understanding what linq to write to have it generated. IQueryable<T> will be missed though.
Is there a way in NHibernate to start with an unproxied model
var m = new Model() { ID = 1 };
m.Name = "test";
//Model also has .LastName and .Age
Now save this model only updating Name without first selecting the model from the session?
If model has other properties then name, you need to initialize these with the original value in the database, unless they will be set to null.
You can use HQL update operations; I never tried it myself.
You could also use a native SQL statement. ("Update model set name ...").
Usually, this optimization is not needed. There are really rare cases where you need to avoid selecting the data, so writing this SQL statements are just a waste of time. You are using an ORM, this means: write your software object oriented! Unless you won't get much advantages from it.
What Stefan says looks like what you need. Please be aware that this is really an edge case and you should be happy with fully loading your entity unless you have some ultra-high-performance issues.
If you simply don't want to hit the database - try using caching - entity cache is very simple and efficient.
If your entity is a huge one - i.e. it contains a blob or something - think about splitting it in two (with many-to-one so that you can utilize lazy loading).
http://www.hibernate.org/hib_docs/nhibernate/html/mapping.html
dynamic-update (optional, defaults to
false): Specifies that UPDATE SQL
should be generated at runtime and
contain only those columns whose
values have changed.
Place dynamic-update on the class in the HBM.
var m = new Model() { ID = 1 };
m = session.Update(m); //attach m to the session.
m.Name = "test";
session.Save(m);