var myObjectList = (List<MyObject>)JsonConvert.DeserializeObject(strResponseMessage, typeof(List<MyObject>));
the above works to deserialise a JSON string to a list of custom objects when the JSON has the following format
[
{
"Name": "Value"
},
{
"Name": "Value"
},
{
"Name": "Value"
},
"Name": "Value"
}
]
I don't know how to do the same when the format is like this
{
"ReturnedData" : [
{
"Name": "Value"
},
{
"Name": "Value"
},
{
"Name": "Value"
},
"Name": "Value"
}
]
}
I can get the data like this
JObject information = JObject.Parse(strResponseMessage);
foreach (dynamic data in information)
{
//convert to object here
}
and that works for Android but it seems that you cannot use a type of 'dynamic' for iOS as I get the error:
Object type Microsoft.CSharp.RuntimeBinder.CSharpInvokeMemberBinder cannot be converted to target type: System.Object[]
What step am I missing to convert the second JSON string to the first?
If JsonConvert is JSON.Net just instead of List use
public class MyClass {
public List<MyObject> ReturnedData { get; set; }
}
You can't use the dynamic keyword on iOS as its forbidden to generate code as it states in this link.
Quote:-
No Dynamic Code Generation
Since the iPhone's kernel prevents an application from generating code dynamically Mono on the iPhone does not support any form of dynamic code generation.
These include:
The System.Reflection.Emit is not available.
Quote:-
System.Reflection.Emit
The lack of System.Reflection. Emit means that no code that depends on runtime code generation will work. This includes things like:
The Dynamic Language Runtime.
Any languages built on top of the Dynamic Language Runtime.
Apparently there is some support creeping in from v7.2 as can be seen in this link - See #Rodja answer. - however - its very experimental and has flaws preventing this from fully working.
Your best approach would be to process the JObject - without - reying on the dynamic keyword and you will be alright on both Android and iOS.
Thanks for your replies - I was able to solve it as follows
JObject information = JObject.Parse(strResponseMessage);
string json = JsonConvert.SerializeObject(strResponseMessage["ReturnedData "]);
var myObjectList = (List<MyObject>)JsonConvert.DeserializeObject(json , typeof(List<MyObject>));
Works perfectly!
Related
I want to store various data for my app in a single place, in a map. In JS, I'd store in a JSON file, and I want to use the same sort of approach, but struggling with Dart. I can't seem to work with nested lists or maps.
Here's essentially what I want to do:
var items = {
"item1": {
"message" : "aa",
"nested1": {
"message": "bb",
"nested2" : {
"message" : "cc"
},
}
},
};
void main() {
var message1 = items["item1"]?["message"];
print(message1);
print(message1.runtimeType);
var message2 = items["item1"]?["nested1"]?["message"];
print(message2);
print(message2.runtimeType);
var message3 = items["item1"]?["nested1"]?["nested2"]?["message"];
print(message3);
print(message3.runtimeType);
}
I've been struggling to make this work in Dartpad.
message1 works as expected, but then I can't seem to work my way down the tree...
Is this a shortcoming with map literals? Do I need to use constructors? Or am I missing something bigger?
Your problem is that items is inferred to be of type Map<String, Map<String, Object>>, but Object does not have an operator []. Therefore when you eventually extract that Object, you will not be able to do anything with it until you cast it a more specific type.
What you probably want instead is to explicitly declare items as Map<String, dynamic> to disable static type-checking on the Map's values:
var items = <String, dynamic>{
"item1": ...
};
Of course, when you disable static type-checking, you are responsible for ensuring that the values you get from the Map are what you expect, or you will get NoSuchMethod or TypeError exceptions at runtime. If you do want static type-checking, you should use define custom classes instead of using a blob of key-value properties.
I'm new to MongoDB as well as to MongoDB Realm Sync. I was following the Realm Sync tutorial and Realm data model docs, but I wanted to learn more so I tweaked the Atlas collection structure as follows.
Projects > Tasks // i.e. tasks is a sub-collection in each project.
What I don't know is how to come up with Realm Sync Schema which can support Atlas sub-collections.
The best I came up with is a Schema where Tasks are modelled as an array within the Project. But, I'm worried that this can hit the 16MB (although a lot!) document limit for projects with a lot of the tasks.
{
"bsonType": "object",
"properties": {
"_id": {
"bsonType": "objectId"
},
"_partition": {
"bsonType": "string"
},
"name": {
"bsonType": "string"
},
"tasks": {
"bsonType": "array",
"items": {
"bsonType": "object",
"title": "Task",
"properties": {
"name": {
"bsonType": "string"
},
"status": {
"bsonType": "string"
}
}
}
}
},
"required": [
"_id",
"_partition",
"name",
],
"title": "Project"
}
Looking forward on how to model sub-collection the right way.
Edit
Here's my client side Realm models.
import Foundation
import RealmSwift
class Project: Object {
#objc dynamic var _id: String = ObjectId.generate().stringValue
#objc dynamic var _partition: String = "" // user.id
#objc dynamic var name: String = ""
var tasks = RealmSwift.List<Task>()
override static func primaryKey() -> String? {
return "_id"
}
}
class Task: EmbeddedObject {
#objc dynamic var name: String = ""
#objc dynamic var status: String = "Pending"
}
As far the CRUD operations are concerned, I only create a new project and read existing projects as follows.
// Read projects
realm.objects(Project.self).forEach { (project) in
// Access fields
}
// Create a new project
try! realm.write {
realm.add(project)
}
Your code looks great and your heading the right direction, so this answer is more explanation and suggestions on modeling than hard code.
First, Realm objects are lazily loaded which means they are only loaded when used. Tens of thousands of objects will have very little impact on a devices memory. So suppose you have 10,000 users and you 'load them all in'
let myTenThousandUsers = realm.objects(UserClass.self)
meh, no big deal. However, doing this
let someFilteredUsers = myTenThousandUsers.filter { $0.blah == "blah" }
will (could) create a problem - if that returns 10,000 users they are all loaded into memory possibly overwhelming the device. That's a Swift function and 'converting' Realms lazy data using Swift should generally be avoided (use case dependent)
The observation of this code using Swift .forEach
realm.objects(Project.self).forEach { (project) in
// Access fields
}
could cause issues depending on what's being done with those project objects - using them as a tableView dataSource could be trouble if there are a lot of them.
Second thing is the question about the 16Mb limit per document. For clarity an Atlas document is this
{
field1: value1,
field2: value2,
field3: value3,
...
fieldN: valueN
}
where value can be any of the BSON data types such as other documents, arrays, and arrays of documents.
In your structure, the var tasks = RealmSwift.List<Task>() where Task is an embedded object. While conceptually embedded objects are objects, I believe they count toward a single document limit because they are embedded (correct me if I am wrong); as the number of them grows, the size of the enclosing document grows - keeping in mind that 16Mb of text is an ENORMOUS of text so that would/could equate to millions of tasks per project.
The simple solution is to not embed them and have them stand on their own.
class Task: Object {
#objc dynamic var _id: String = ObjectId.generate().stringValue
#objc dynamic var _partition: String = ""
#objc dynamic var name: String = ""
#objc dynamic var status: String = "Pending"
override static func primaryKey() -> String? {
return "_id"
}
}
Then each one can be 16Mb, and an 'unlimited number' can be associated with a single project. One advantage of embedded objects is a type of cascade delete where when the parent object is deleted, the child objects are as well, but with a 1-many relationship from Project to Tasks - deleting a bunch of tasks belonging to a parent is easy.
Oh - another case for not using embedded objects - especially for this use case - is they cannot have indexed properties. Indexing can greatly speed up some queries.
I have a web-service which returns student and enrolled class details.
{
"name": "student-name",
"classes": [
{
"className": "reactor-101",
"day": "Tuesday"
},
{
"className": "reactor-102",
"day": "Friday"
}
]
}
The DTO for this class is as below:
public class Student {
private String name;
private Flux<StudentClass> classes;
#Data
#AllArgsConstructor
#JsonInclude(JsonInclude.Include.NON_DEFAULT)
public static class StudentClass {
private String className;
private String day;
}
}
The main REST controller logic to fetch the student is as follows:
Flux<StudentClass> studentClassFlux = studentClassRepository.getStudentClass(studentName);
return Mono.just(new Student(studentName, studentClassFlux));
The problem with this is, I get the following output after making the REST call:
{
"name": "student-name",
"classes": {
"prefetch": 32,
"scanAvailable": true
}
}
I can achieve the desired output by blocking on the flux request to get completed and then convert the output to list.
List<StudentClass> studentClassList = studentClassRepository.getStudentClass(studentName)..toStream().collect(Collectors.toList());
return Mono.just(new Student(studentName, studentClassList)); // Change the Student#classes from flux to list
I am new to reactive-programming.
What is the correct way of using the Flux & Mono here to get the desired output?
Reactive types aren't meant to be serialized when wrapped in each other.
In that particular case, you probably want your Student object to contain a List<StudentClass>. You can achieve that like this:
public Mono<Student> findStudent(String studentName) {
return studentClassRepository
.getStudentClass(studentName)
.collectList()
.map(studentClasses -> new Student(studentName, studentClasses));
}
I think, in the case that you really need a Flux in your result, you would want to break down the API so that you have separate methods to retrieve the entities.
One for student properties, and another for their classes. The student GET method could be a Mono, while the classes would return a Flux.
I tried the following code in Avro IDL which references the logical type timestamp-millis and it doesn't work.
Is there an import required to use logical types in Avro IDL? Or are logical types not useable, and I need to use the primitive type (long in this case) instead?
protocol test {
record test {
timestamp-millis time;
}
}
Results in:
Exception in thread "main" org.apache.avro.compiler.idl.ParseException: Undefined name 'timestamp', at line 3, column 9
This works of course:
protocol test {
record test {
long time;
}
}
You can use a generic annotation:
protocol test {
record test {
#logicalType("timestamp-millis")
long time;
}
}
There's actually also a shorthand you can use for timestamp-millis and a handful of other logical types (the documentation hasn't been released yet, see here for the full list of aliases):
protocol test {
record test {
timestamp_ms time;
}
}
LogicalType timestamp-millis is used with type long, so you may use schema like this:
{
"type" : "record",
"name" : "Test",
"fields" : [ {
"name" : "time",
"type" : {
"type" : "long",
"logicalType" : "timestamp-millis"
}
}]
}
I have a huge Neo4j database that I created using the batch import tool. Now I want to expose certain parts of the data via APIs (that will run a query in the backend) to my users. My requirements are pretty general:
1. Latency should be minimum
2. Support qps of about ~10-20.
Can someone give me recommendations on what I should use for this and any documentation on how to go about this? I see several examples of ruby/rails and REST APIs -- however they are specific to exposing the data as is without any complex queries in the backend. I am not sure how to translate that into the specific APIs that I want. Any help would be appreciated.
Thanks.
I wrote a simple Flask API example that interfaces with Neo4j for a simple demo (backend for a messaging iOS app).
You might find it a helpful reference: https://github.com/johnymontana/messages-api
There are also a few resources online for using Flask with Neo4j:
http://nicolewhite.github.io/neo4j-flask/
http://neo4j.com/blog/building-python-web-application-using-flask-neo4j/
https://github.com/nicolewhite/neo4j-flask
Check out the GraphAware Framework. You can build the APIs directly on top of Neo4j (same JVM) but you have to use Cypher, Java, or Scala.
I'd start with Cypher, because you can write it very quickly, then optimise for performance, and finally, if all else fails and your latency is still to high, convert to Java.
You can expose subgraphs (or even partially hydrated nodes and relationship, i.e. only certain properties) very easily. Checkout out the stuff in the api package. Example code:
You'd write a controller to return a person's graph, but only include nodes' names (not ages or anything else):
#RestController
public class ApiExample {
private final GraphDatabaseService database;
#Autowired
public ApiExample(GraphDatabaseService database) {
this.database = database;
}
#RequestMapping(path = "person/{name}")
public JsonGraph getPersonGraph(#PathVariable(value = "name") String name) {
JsonGraph<?> result = new JsonGraph() {
#Override
protected JsonGraph self() {
return this;
}
};
try (Transaction tx = database.beginTx()) {
Node person = database.findNode(label("Person"), "name", name);
if (person == null) {
throw new NotFoundException(); //eventually translate to 404
}
result.addNode(person, IncludeOnlyNameNodeTransformer.INSTANCE);
for (Relationship worksFor : person.getRelationships(withName("WORKS_FOR"), Direction.OUTGOING)) {
result.addRelationship(worksFor);
result.addNode(worksFor.getEndNode(), IncludeOnlyNameNodeTransformer.INSTANCE);
}
tx.success();
}
return result;
}
private static final class IncludeOnlyNameNodeTransformer implements NodeTransformer<LongIdJsonNode> {
private static final IncludeOnlyNameNodeTransformer INSTANCE = new IncludeOnlyNameNodeTransformer();
private IncludeOnlyNameNodeTransformer() {
}
#Override
public LongIdJsonNode transform(Node node) {
return new LongIdJsonNode(node, new String[]{"name"});
}
}
}
Running this test
public class ApiExampleTest extends GraphAwareApiTest {
#Override
protected void populateDatabase(GraphDatabaseService database) {
database.execute("CREATE INDEX ON :Person(name)");
database.execute("CREATE (:Person {name:'Michal', age:32})-[:WORKS_FOR {since:2013}]->(:Company {name:'GraphAware', est:2013})");
}
#Test
public void testExample() {
System.out.println(httpClient.get(baseUrl() + "/person/Michal/", 200));
}
}
would return the following JSON
{
"nodes": [
{
"properties": {
"name": "GraphAware"
},
"labels": [
"Company"
],
"id": 1
},
{
"properties": {
"name": "Michal"
},
"labels": [
"Person"
],
"id": 0
}
],
"relationships": [
{
"properties": {
"since": 2013
},
"type": "WORKS_FOR",
"id": 0,
"startNodeId": 0,
"endNodeId": 1
}
]
}
Obviously you can roll your own using frameworks like Rails / Sinatra. If you want a standard for the way that your API is formatted I quite like the JSON API standard:
http://jsonapi.org/
Here is an episode of The Changelog podcast talking about it:
https://changelog.com/189/
There's also a gem for creating resource objects which determine what is exposed and what is not:
https://github.com/cerebris/jsonapi-resources
I tried it out a bit with the neo4j gem and it works at a basic level, though once you start getting into includes there seems to be some dependencies on ActiveRecord. I'd love to see issues like that worked out, though.
You might also check out the GraphQL standard which was created by Facebook:
https://github.com/facebook/graphql
There's a Ruby gem for it:
https://github.com/rmosolgo/graphql-ruby
And, of course, another episode of The Changelog ;)
http://5by5.tv/changelog/149
Various other API resources for Ruby:
https://github.com/webmachine/webmachine-ruby
https://github.com/ruby-grape/grape
Use grest.
You can simply define your primary model(s) and its relation(s) (as secondary) and build an API with minimal coding and as quickly as possible!