I am new programmer student, now i develop mobile app with phonegap. So I use sqlite and persistence js.but I don't know how to write "inner join" in persistence js function. Hope all of you help me.
Take a look at documentation:
https://github.com/zefhemel/persistencejs
Some text from it:
The methods to define relationships to other entities:
EntityName.hasMany(property, Entity, inverseProperty)
defines a 1:N or N:M relationship (depending on the inverse property).
EntityName.hasOne(property, Entity)
defines a 1:1 or N:1 relationship.
If an object has a hasOne relationship to another which has not yet been fetched from the database (e.g. when prefetch wasn't used), you can fetch in manually using fetch. When the property object is retrieved the callback function is invoked with the result, the result is also cached in the entity object itself.
obj.fetch(prop, callback)
Related
Completely new to Axon here.
I have a class defined in Kotlin:
data class ProjectedQuote(
#Id var submissionId: String,
var periodId: String,
var accountNumber: String
)
It gets instantiated and updated by event handlers, then it is returned in response to queries.
I'm needing to create a query that finds a ProjectedQuote instance by accountNumber, not id. I'm not sure how to do that.
To date, I've only done queries like:
SELECT q FROM ProjectedQuote q WHERE q.id LIKE CONCAT(:idStartsWith, '%') ORDER BY q.id
My narrowly-focused question is:
How do I write a query that finds ProjectedQuote using accountNumber instead of id?
My broader question is:
How can I see what fields are available to query by in the Axon databases?
Query messages typically read data from the view models created by the event listeners. Event listeners typically execute logic based on decisions that have been made by the command model. Usually, this involves updating view models or forwarding updates to other components.
So the mechanism for creating and receiving views is entirely up to you. (jpa, spring data, mybatis, jdbc etc.) A good example the axon project is https://github.com/idugalic/digital-restaurant
What Sergey points out here too is very valid.
How you model your Query Model in such an application is entirely up to you. So pick JPA, JDBC, MongoDB, ElasticSearch, Neo4j..whichever format of containing the Query Model suites you best!
This freedom of storage mechanisms thus also points out that your Query Model isn't stored in an 'Axon Database'; it's stored in the database you have chosen.
In regards to how to model your queries, you could have a look at how QueryMessages and QueryHandlers can be used in Axon, over here. This is just another dedicated type of message from Axon's perspective, just like Command- and EventMessages.
Using Query Messages, you can specify the type of query you'd want to perform as a separate object, which is the query.
This query will in turn be handled by an #QueryHandler annotated function.
The #QueryHandler annotated function will in turn perform the actual operation to retrieving the model from the database you have chosen to use to store the model in.
Hope this gives you some insights!
Iterations of this question have been asked in the past, but this presents unique challenges as it combines some of the issues in one larger problem.
I have an entity(User) that is used as the user class in my application, then I have another entity (UserExtra), in a one-to-one relationship with the user entity, UserExtra's id is the same as User. The foreign key is the same as the primary key.
When the user object is loaded (say by $this->getUser() or by {{ app.user }}, the UserExtra data is also loaded through a join. The whole point of having two entities is so I don't have to load all the data at once.
I even tried defining a custom UserLoaderInterface/UserProviderInterface Repository for User, making sure that refreshUser and loadUserByUsername would only load the User data (I'd like for the UserExtra data to sit in a proxy unless I explicitly need it) but when Doctrine goes to Hydrate the object, it issues an extra query to load the UserExtra data, thereby skipping the Proxy status.
Is there a way out of this?
there are many solution for your issue:
1) Change the owning side and inverse side http://developer.happyr.com/choose-owning-side-in-onetoone-relation - I don't think that's right from a DB design perspective every time.
2) In functions like find, findAll, etc, the inverse side in OneToOne is joined automatically (it's always like fetch EAGER). But in DQL, it's not working like fetch EAGER and that costs the additional queries. Possible solution is every time to join with the inverse entity
3) If an alternative result format (i.e. getArrayResult()) is sufficient for some use-cases, that could also avoid this problem.
4) Change inverse side to be OneToMany - just looks wrong, maybe could be a temporary workaround.
5) Force partial objects. No additional queries but also no lazy-loading: $query->setHint (Query::HINT_FORCE_PARTIAL_LOAD, true) - seams to me the only possible solution, but not without a price:
Partial Objects are a little bit risky, because your entity behavior is not normal. For example if you not specify in ->select() all associations that you will user you can have an error because your object will not be full, all not specifically selected associations will be null
6) Not mapping the inverse bi-directional OneToOne association and either use an explicit service or a more active record approach - https://github.com/doctrine/doctrine2/pull/970#issuecomment-38383961 - And it looks like Doctrine closed the issue
this question may help you : one to one relation load
I have 2 entities, User and Profile. Profile has in-symfony relation with User, but there is no in-database relation (no foreign key, no cascade) - only simple int column named user_id and nothing more.
Problem is obvious: when i delete user - associated profiles persists, but their user_id points to non-existing user row.
Since I use in-symfony relations when i fetch profile from database it fetches also related user entity. I expected that if there is no row with specific ID, it would just leave null or at least throw an exception or something.
Problem is that symfony creates empty User entity object with only id set. rest of its fields are null.
I know solution would be to create FK, constraints etc ... but I'm not allowed to touch anything in database schema.
How can I manage this problem ? I could even leave those empty object if only i had simple way to determine if they exist in database inside TWIG - so i would know if i can display {{ profile.user.email }} for example.
Fast and dirty solution, as you ask, is to use this test: http://twig.sensiolabs.org/doc/tests/defined.html
But I strongly recommend to rework your entity relations.
Found solution: its fetch: EAGER set to problematic mapping in doctrine.
By default doctrine uses LAZY fetching what results in using Proxy classes generated by doctrine for related entity. That class is almost same as real entity class. Difference is inside getter methods that before returning value performs fetching entity from database.
At this point, when you call getter on such proxy, doctrine tries to find entity in database using its ID, and since it doesn't find anything it throws exception.
When using EAGER fetching doctrine performs fetching of related entities on the same time when it fetches main entity and if it doesn't find it then sets null on relation field.
Am I missing a point with Doctrine? It's been very useful for some scenarios, but for the basic scenario of retrieving an entity using an Id (say using find() or findOneBy()) why do you see a query being fired off for every relationship to populate the main entity's properties?
Surely with the mapping/annotations I've created, Doctrine should be capable of a few joins and one query, without having to write a DQL query for the retrieval of each entity.
Or, as I'm predicting, have I missed the point somewhere!
Just add the aliases of related entities to select part of your query.
Let’s say, you have Book related one-to-many to Cover, and you want so select some books with their covers.
With query builder, use:
->createQueryBuilder()
->select("book, cover")
->from("Book", "book")
->leftJoin("book.covers", "cover")
With query, use:
SELECT book, cover FROM Book book LEFT JOIN book.covers cover
As the result, you will receive collections of Book with prepopulated $covers collection.
Because the relationships are hydrated only when needed - by default Doctrine uses a lazy-loading strategy.
If you already know that you will access the related entities, you should build a DQL query that retrieves the record AND the related entities.
I'm trying to create a many-to-many relationship in Entity Framework (code first), according to the following post: Database design for limited number of choices in MVC and Entity Framework?
However, I can't get it to work properly, and I'm sure I'm doing something very simple the wrong way. Here's the diagram I have no from my attempts:
The point of the junction table is that I need to have an extra property, Level, in the relationship, so I can't just go with a direct relationship between Consultant and Program. I added the ConsultantProgramLink entity manually in the designer, and then added associations to Program and Consultant respectively, selecting to add a FK for each, and then made them both primary keys. But when I do it like this it doesn't work as I expected:
If I had done a direct association between Consultant and Program, I would have been able to refer to, say, Consultant.Programs in my code. But that doesn't work now with the junction table. Is there any way to remedy this, or do I always have to go through the junction property (Consultant.ConsultantProgramLink.Programs)? In any case, even if I do try to go through the junction property it doesn't help. I can do Consultant.ConsultantProgramLink in my code, but another dot doesn't give me the navigation property Programs (which for some reason also became simply Program, why? Can I just rename them if I eventually get access to them at all?).
So what am I doing wrong? Why can't I access the properties through dot notation in my code?
Once you model a junction table as an entity you indeed lose direct many-to-many relation between Consultant and Program. That is how it works. You will either have direct many-to-many relation or additional properties in the junction table. Not both. If you want both you can try creating custom Programs property on Consultant and use linq query to get related programs:
public IEnumerable<Program> Programs
{
get
{
return this.ConsultantProgramLinks.Select(l => l.Program);
}
}
The example is also the explanation of your last problem. You can't have Program property on ConsultantProgramLink because it is a collection of related entities, not single entity (it should be called ConsultantProgramLinks). The property in ConsultantProgramLink entity is called simply Programbecause it represents single entity not collection.
Edit:
If you need each Program to be automatically associated with each Consultant you must enforce it when you are going to create new Program. Having junction table exposed as separate entity will probably allow you achieving it easily:
var program = new Program();
...
context.Programs.AddObject(program);
var ids = from c in context.Consultants
select c.Id;
foreach (var id in ids)
{
var link = new ConsultantProgramLink
{
ConsultantId = id,
Program = program
};
context.ConsultantProgramLinks.AddObject(link);
}
context.SaveChanges();
If you add new Consultant you will have to create links to all programs in the same way.
The disadvantage is that if you have for example 1000 consultants this construct will create 1001 database inserts where each insert will be executed in separate roundtrip to the database. To avoid it the only option is either use stored procedur or trigger on Program table.