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How to save a struct to realm in swift?
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Closed 6 years ago.
Since Swift Protocol Oriented Programming, struct, value typed and functional programming are improving in Swift. But how about the databases. I have used 2 database: Cora Data and Realm. Both required a class to be inherited from Object (Realm) or ManagedObject(Core Data)
My question is: What is the database model to use If I want to design my application model with struct only?
Thanks
This was asked in a similar question before: How to save a struct to realm in swift?
Suffice it to say, Realm's implementation details (and Core Data as well) rely on the Objective-C runtime, so their models cannot be structs.
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Edited
Having multiple data sources for an app
What is the best approach to combine all data sources together in one class and add it as one environment object, keeping in mind data might change, therefore objects update the views?
What are the appropriate Bindings to use for:
Services (API fetches): #Published?
Computed variables: Lazy var?
Please refer to the diagram as an example. Thanks.
These questions were good references:
An equivalent to computed properties using #Published in Swift Combine?
https://medium.com/genetec-tech/property-wrappers-in-swift-5-1-the-missing-published-implementation-1a466ebcf660
diagram
So, you should use a layered architecture and you will not have those problems.
service layer, it's the lowest layer reads the data from either web or db, or other services
repository layer gets the data from service and process it, caching, etc
usecase layer combines data from multiple repositories
viewmodel layer gets the data from usecase and sends it to view
each service or repository handles one type of data "Users" for example
now, if you need to combine multiple types of data, like Users and Companies let's say, you need a Usecase layer which will combine all the data
on your viewmodel you only use the usecase layer
One important note, passed objects change between layers, so on service layer you have UserDto (coming from webservice), and UserEntity (coming from DB), the repo will transform those in UserResponse, which you don't know if it's db or webservice and even more the UseCase will transform UserResponse and CompanyReponse into a User object which will be passed to ViewModel and will contain all data required there.
Also, until you get to the viewmodel layer you should not need SwiftUI, if you need it, you are doing something wrong, use Swift Combine to handle data.
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I know there is scala.collection.mutable package which provides mutable data structures. But how is it done?
Can I write my own mutable data structure and pass it to a function to be changed?
Edit: The question aims towards techniques that can be used to implement mutable data types.
Read this wonderful tutorial on implementing custom collections in scala.
It should have all you need to answer the question "how it is done".
If you are just talking about any data structure, not a collection, then something like
class Foo(var bar: String)
will do. But ... don't do it. While, there are rare and isolated cases, where having a mutable structure is unavoidable, chances are, you will not encounter such a case for a long time.
My advice to you is to start with learning to write good, idiomatic scala code, and getting into the functional mindset, where data structures don't mutate under you. Learn to appreciate that.
Sure, you can. There is no limitation, that all immutable data structures should be inside scala.collection.immutable, and all mutable DS should be inside scala.collection.mutable. Standard collection classes are divided into these two packages just for convenience. You can create your classes, where you like to do it.
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How to store custom objects in Dataset?
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Closed 6 years ago.
I want to implement a generic encoder because I have a small project on Spark 1.6 and when I migrate it to the spark 2.0 its giving me the warning and error
of
Unable to find encoder for type stored in a Dataset. Primitive types (Int, String, etc) and Product types (case classes) are supported by importing spark.implicits._ Support for serializing other types will be added in future releases.
at many places hence I want to implement a generic encoder and put it in package object. I just want to know how can I implement a generic Encoder in spark 2.0 ?
Developing custom encoders usually starts with composing existing encoders from org.apache.spark.sql.Encoders object.
Please note that many places in Spark check whether the encoder in use is an instance of ExpressionEncoder (i.e. SparkSession.createDataset) so you may want to review expression encoders as the base for custom development.
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Code-first vs Model/Database-first [closed]
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What is the difference between 'Database First' and 'Code First to Existing Database' in Entity Framework
(1 answer)
Closed 8 years ago.
I'm new to MVC and am not seeing the difference between Code First and Model First. They seem to be the same thing to me: you write out the classes that will become the domain model and MVC creates the database automatically for you.
I don't see a difference between these two approaches. What am I missing here?
There are no differences. Model First or Code First just represent the approaches that programmers can adopt (or database first ).
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Closed 11 years ago.
Possible Duplicate:
What is the difference between Type and Class?
What is the relationship between class and type? Or what are the relationships between class and type?
If you think defining the concepts class and type clarifies the answer, please include definitions.
Resuming:
The basic relationship between those two concepts is that a class defines a type.
If you define the class Car, you're also defining a new type: Car.