I have a java project
I have a nebula graph to save all my information
I need to have graphql queries
I implement it but we need a dynamic schema
so we save our schema for any of dynamic entity types
for example
our users want to have dynamic datatypes that we implement and save in nebula graph
our users can save vertex as items
after that we need to have endpoint for query in our all vertex that saved by those data types
https://dgraph.io/docs/graphql/queries/search-filtering/
we need to post our request like this
how can we implement it better
we have a good cache of our datatypes in the java layer.
is there any suggestion for us?
For now, there is no GraphQL support/parsing layer implementation for NebulaGraph.
For java connector, there are some abstraction layers there, could you take a look at them?
https://github.com/nebula-contrib/graph-ocean
https://github.com/nebula-contrib/ngbatis
https://github.com/nebula-contrib/nebula-jdbc
Also, equivlant queries(towards graphql) could be composed, too to return complex things in OpenCypher.
Related
What is the practical difference between merging and stitching GraphQL schemas? The graphql-tools documentation (merging:https://www.graphql-tools.com/docs/schema-merging, stitching:https://www.graphql-tools.com/docs/schema-stitching/stitch-combining-schemas) is a bit ambiguous when it comes exactly to each implementation's use cases. If I understood correctly, stitching is just a matter of organizational preferences and each subscheme becomes a 'proxy' to your scheme, while the merge functionality seems pretty similar to me. Could you please explain the difference? Thank you!
Schema stitching is used when you want to retrieve data from multiple GraphQL APIs in the same query (which is basically the motivation behind GraphQL).
For example, you may have to extract data from two GraphQL APIs - one which offers you information about the location, the other GraphQL API gives information about the weather. For you to execute a query that has access to both endpoints at the same time, you have to STITCH the schemas of the two endpoints, which will allow you to perform a query like this(which presents a link between the two endpoints as well) :
{
event(id: "5983706debf3140039d1e8b4") {
title
description
url
location {
city
country
weather {
summary
temperature
}
}
}
}
On the other hand, schema merging refers to gathering all your schemas that have been split based on domains, mainly for organizational purposes. Schema merging does not keep the individual subschemas.
One advantage of Document DBs like Couchbase is schemaless entities. It gives me freedom to add new attributes within the document without any schema change.
Using Couchbase JsonObject and JsonDocument my code remains generic to perform CRUD operations without any need to modify it whenever new attribute is added to the document. Refer this example where no Entities are created.
However if I follow the usual Spring Data approach of creating Entity classes, I do not take full advantage of this flexibility. I will end up in code change whenever I add new attribute into my document.
Is there a approach to have generic entity using Spring Data? Or Spring Data is not really suitable for schemaless DBs? Or is my understanding is incorrect?
I would argue the opposite is true.
One way or another if you introduce a new field you have to handle the existing data that doesn't have that field.
Either you update all your documents to include that field. That is what schema based stores basically force you to do.
Or you leave your store as it is and let your application handle that issue. With Spring Data you have some nice and obvious ways to handle that in a consistent fashion, e.g. by having a default value in the entity or handling that in a listener.
I'm looking for a solution with Spring / camel to consume multiple REST services during runtime and create tables to store the data from REST API and compare the data dynamically. I don't know the schema for JSON API in advance to generate the JAVA client classes to create JPA persistent entity classes during run time.
You'll need to think through this differently. Id forget about Java class POJOs that you don't have and can't create since the class structure isn't known in advance. So anything with POJO->Entity binding would be pretty useless.
One solution is to simply parse the xml or json body manually with en event-based parser (like SAX for XML) and simply build an SQL create string as you go through the document. Your field and table names would correspond to the tags in the document. Without access to an XSD or other structure description, no meta data is available for field lengths or types. Make everything really long VARCHAR? Also perhaps an XML or other kind of database might suite your problem domain better. In any case, you could include such a thing right in your Camel route as a Processor that will process the body and create the necessary tables if they don't already exist. You could even alter a table for lengths in the process when you have a field value that is longer than what's currently defined.
For application developers, I suppose the traditional paradigm for writing an application with domain objects that can be persisted to an underlying data store (SQL database for arguments sake), is to write the domain objects and then write (or generate) the table structure. There is a tight coupling between what the domain object looks like and what the structure of underlying data store looks like. So if you want to add a piece of information to your domain object, you add the field to your code and then add a column to the appropriate database table. All familiar?
This is all well and good for data stores that have a well defined structure (I'm mainly talking about SQL databases whereby the tables and columns are pre-defined and fixed), but now a number of alternatives to the ubiquitous SQL database exist and these often do not constrain the data in this way. For instance, MongoDB is a NoSQL database whereby you divide data into collections but aside from that there is no structuring of the data. You don't define new columns when you want to add a new field.
Now to the question: given the flexibility of a data store like MongoDB, how would one go about achieving a similar kind of flexibility in the domain objects that represent this data? So for instance if I'm using Spring and creating my own domain obejcts, when I add a "middleName" field to my data, how can I avoid having to add a "middleName" field to my domain object? I'm looking for some kind of mechanism/approach/framework to dynamically inspect the data and have access to it in my domain object without having to make a code change every time. All ideas welcome.
I think you have a couple of choices:
You can use a dynamic programming language and not have domain objects (clojure for example)
If you're fixed on using java, the mongo java driver returns data in DBObject which is essentially a Map. So the default behavior already provides what you want. It's only when you map the DBObject into domain objects, using a library like morphia (or spring-data), that you even have to worry about domain objects at all.
But, if I was using java, I would stick with the standard convention of domain objects mapped via morphia, because I think adding a field is a very minor inconvenience when compared against the benefits.
I think the question is inherintly paradoxical-
On one hand, you want to have domain objects, i.e. objects that represent the data (and behaviour) of your problem domain.
On the other hand, you say that you don't want your domain objects to be explicitly influenced by changes to the data.
But when you have objects that represent your problem domain, you want to do just that- to represent your problem domain.
So that if, for example, middle name is added, then your representation of the real-life 'User' entity should change to accomodate this change to the real-life user; perhaps not only by adding this piece of data to your object, but also adding some related behaviour (validation of middle name, or some functionality related to it).
In essense, what I'm trying to say here is that when you have (classic OO) domain objects, you may need to change your behaviour / functionality along with your data, and since you don't have any automatic way of changing your behaviour, the question of automatically changing your data becomes irrelevant.
If you don't want behaviour associated with your data, then you essentialy have DTOs, and #Kevin's answer is what you're looking for.
Honestly, it sounds more like you're looking for some kind of blackbox DTO where, like you describe, fields are added or removed "arbitrarily" depending on the data. This makes me inclined to suggest a simple Map to do the job. You can't really have a domain-driven design if your domain model is constantly changing.
I am building a DataAccess layer to a DB, what data structure is recommended to use to pass and return a collection?
I use a list of data access objects mapped to the db tables.
I'm not sure what language you're using, but in general, there are tradeoffs of simplicity vs extensibility.
If you return the DataSet directly, you have now coupled yourself to database specific classes. This leaves little room for extension - what if you allow access to files or to other types of data sources? But, it is also very simple. This is the recordset pattern and C#/VB provide a lot of built-in support for this. The GUI layer can access the recordset and easily manipulate the data. This works well for simple applications.
On the other hand, you can wrap the datasets in a custom object, and provide gateway methods (see the Gateway pattern http://martinfowler.com/eaaCatalog/gateway.html). This method is more complex, but provides a lot more extensibility. In a larger application when you need to separate the the business logic, data logic, and GUI logic, this is a more robust way to go.
For larger enterprise applications, you can look into using Object Relational Mapping tools (ORM). They help to automatically map java objects to database tables. They hide a lot of the painful SQL details. Frameworks such as Spring provide excellent support for ORMs.
I tend to use arrays of objects, so that I can disconnect the DAO from the business logic.
You can store the data in the DAO as a dataset, for example, and give them an easy way to add to the database before doing an update, so they can pass in information to do modification operations, and then when they want to commit the changes they can do it in one shot.
I prefer that the user can't add/modify the structure themselves, as it makes it harder to determine what must be changed in the database.
By initially returning an array they can then display what is in the database.
Then, as the presentation layer makes changes, the DAO can be updated by the controller. By having a loose coupling the entire system becomes more flexible, as you can change the DAO from a dataset to something else, and the rest of the application doesn't care.
There are two choices that are the most generic.
The first way to look at a ResultSet is as a List of Maps, where each Map represents a row in the ResultSet. The keys are the columns listed in the FROM clause; the values are the database values.
The second way to look at a ResultSet is as a Map of Lists, where each List represents a column in the ResultSet. The Map keys are the columns listed in the FROM clause; the values are the List of database values.
If you don't want to do full-blown ORM, these can carry you a long way.