I'm serializing an object with YamlDotNet with both reference and value types. What i'm looking to accomplish is that my integer values of zero remain in the outputted yaml, but null values would be discarded. EmitDefaults looks to discard '0' for numeric values. i understand null is the default value for reference types. Json.Net solved this with breaking it out into the following properties:
NullValueHandling = NullValueHandling.Ignore,
DefaultValueHandling = DefaultValueHandling.Ignore,
is there any way to accomplish the below?
class foo
{
int index {get;set;}
string bar {get;set;}
}
new foo { index =0; bar = null }
would yield the following yaml:
index: 0
new foo { index =0; bar = "bar" }
would yield the following yaml:
index: 0
bar: bar
Thanks
Not sure this is what you want, but this is how I force all default values to be serialized:
public override string ToString()
{
var builder = new SerializerBuilder();
builder.EmitDefaults(); // Force even default values to be written, like 0, false.
var serializer = builder.Build();
var strWriter = new StringWriter();
serializer.Serialize(strWriter, this);
return strWriter.ToString();
}
Related
In python, I often use strings as templates, e.g.
templateUrl = '{host}/api/v3/{container}/{resourceid}'
params = {'host': 'www.api.com', 'container': 'books', 'resourceid': 10}
api.get(templateUrl.format(**params))
This allows for easy base class setup and the like. How can I do the same in dart?
I'm assuming I will need to create a utility function to parse the template and substitute manually but really hoping there is something ready to use.
Perhaps a TemplateString class with a format method that takes a Map of name/value pairs to substitute into the string.
Note: the objective is to have a generic "format" or "interpolation" function that doesn't need to know in advance what tags or names will exist in the template.
Further clarification: the templates themselves are not resolved when they are set up. Specifically, the template is defined in one place in the code and then used in many other places.
Dart does not have a generic template string functionality that would allow you to insert values into your template at runtime.
Dart only allows you to interpolate strings with variables using the $ syntax in strings, e.g. var string = '$domain/api/v3/${actions.get}'. You would need to have all the variables defined in your code beforehand.
However, you can easily create your own implementation.
Implementation
You pretty much explained how to do it in your question yourself: you pass a map and use it to have generic access to the parameters using the [] operator.
To convert the template string into something that is easy to access, I would simply create another List containing fixed components, like /api/v3/ and another Map that holds generic components with their name and their position in the template string.
class TemplateString {
final List<String> fixedComponents;
final Map<int, String> genericComponents;
int totalComponents;
TemplateString(String template)
: fixedComponents = <String>[],
genericComponents = <int, String>{},
totalComponents = 0 {
final List<String> components = template.split('{');
for (String component in components) {
if (component == '') continue; // If the template starts with "{", skip the first element.
final split = component.split('}');
if (split.length != 1) {
// The condition allows for template strings without parameters.
genericComponents[totalComponents] = split.first;
totalComponents++;
}
if (split.last != '') {
fixedComponents.add(split.last);
totalComponents++;
}
}
}
String format(Map<String, dynamic> params) {
String result = '';
int fixedComponent = 0;
for (int i = 0; i < totalComponents; i++) {
if (genericComponents.containsKey(i)) {
result += '${params[genericComponents[i]]}';
continue;
}
result += fixedComponents[fixedComponent++];
}
return result;
}
}
Here would be an example usage, I hope that the result is what you expected:
main() {
final templateUrl = TemplateString('{host}/api/v3/{container}/{resourceid}');
final params = <String, dynamic>{'host': 'www.api.com', 'container': 'books', 'resourceid': 10};
print(templateUrl.format(params)); // www.api.com/api/v3/books/10
}
Here it is as a Gist.
Here is my solution:
extension StringFormating on String {
String format(List<String> values) {
int index = 0;
return replaceAllMapped(new RegExp(r'{.*?}'), (_) {
final value = values[index];
index++;
return value;
});
}
String formatWithMap(Map<String, String> mappedValues) {
return replaceAllMapped(new RegExp(r'{(.*?)}'), (match) {
final mapped = mappedValues[match[1]];
if (mapped == null)
throw ArgumentError(
'$mappedValues does not contain the key "${match[1]}"');
return mapped;
});
}
}
This gives you a very similar functionality to what python offers:
"Test {} with {}!".format(["it", "foo"]);
"Test {a} with {b}!".formatWithMap({"a": "it", "b": "foo"})
both return "Test it with foo!"
It's even more easy in Dart. Sample code below :
String host = "www.api.com"
String container = "books"
int resourceId = 10
String templateUrl = "$host/api/v3/$container/${resourceId.toString()}"
With the map, you can do as follows :
Map<String, String> params = {'host': 'www.api.com', 'container': 'books', 'resourceid': 10}
String templateUrl = "${params['host']}/api/v3/${params['container']}/${params['resourceId']}"
Note : The above code defines Map as <String, String>. You might want <String, Dynamic> (and use .toString())
Wouldn't it be simplest to just make it a function with named arguments? You could add some input validation if you wanted to.
String templateUrl({String host = "", String container = "", int resourceid = 0 }) {
return "$host/api/v3/$container/$resourceId";
}
void main() {
api.get(templateUrl(host:"www.api.com", container:"books", resourceid:10));
}
I am trying to send binary data, i.e. byte arrays, using yaml. According to the yaml documentation, Yaml Binary Type, this is supported. On the Java side I use SnakeYaml and if a value of byte[] is passed, then the yaml correctly gives !!binary.
This functionality does not seem to be supported "out of the box" in YamlDotNet. The below code snippet creates a sequence of integer values:
IDictionary<string, object> data = new Dictionary<string, object>();
const string value = ":| value: <XML> /n\n C:\\cat";
byte[] bytes = Encoding.UTF8.GetBytes(value);
data.Add(ValueKey, bytes);
// Turn the object representation into text
using (var output = new StringWriter())
{
var serializer = new Serializer();
serializer.Serialize(output, data);
return output.ToString();
}
Output like:
val:\r- 58\r- 124\r- 32\r- 118\r- 97\r- 108\r- 117\r- 101\r- 58\r- 32\r- 60\r- 88\r- 77\r- 76\r- 62\r- 32\r- 47\r- 110\r- 10\r- 32\r- 67\r- 58\r- 92\r- 99\r- 97\r- 116\r
But I would like something more like:
val: !!binary |-
OnwgdmFsdWU6IDxYTUw+IC9uCiBDOlxjYXQ=
Can anyone recommend a workaround?
The preferred way to add support for custom types is to use a custom IYamlTypeConverter. A possible implementation for the !!binary type would be:
public class ByteArrayConverter : IYamlTypeConverter
{
public bool Accepts(Type type)
{
// Return true to indicate that this converter is able to handle the byte[] type
return type == typeof(byte[]);
}
public object ReadYaml(IParser parser, Type type)
{
var scalar = (YamlDotNet.Core.Events.Scalar)parser.Current;
var bytes = Convert.FromBase64String(scalar.Value);
parser.MoveNext();
return bytes;
}
public void WriteYaml(IEmitter emitter, object value, Type type)
{
var bytes = (byte[])value;
emitter.Emit(new YamlDotNet.Core.Events.Scalar(
null,
"tag:yaml.org,2002:binary",
Convert.ToBase64String(bytes),
ScalarStyle.Plain,
false,
false
));
}
}
To use the converter in the Serializer, you simply need to register it using the following code:
var serializer = new Serializer();
serializer.RegisterTypeConverter(new ByteArrayConverter());
For the Deserializer, you also need to register the converter, but you also need to add a tag mapping to resolve the !!binary tag to the byte[] type:
var deserializer = new Deserializer();
deserializer.RegisterTagMapping("tag:yaml.org,2002:binary", typeof(byte[]));
deserializer.RegisterTypeConverter(new ByteArrayConverter());
A fully working example can be tried here
For anyone that's interested.... I fixed this by creating the string myself and adding the !!binary tag, and also doing some clean up. Below is the code.
ToYaml:
IDictionary<string, string> data = new Dictionary<string, string>();
string byteAsBase64Fromat = Convert.ToBase64String("The string to convert");
byteAsBase64Fromat = "!!binary |-\n" + byteAsBase64Fromat + "\n";
data.Add(ValueKey, byteAsBase64Fromat);
string yaml;
using (var output = new StringWriter())
{
var serializer = new Serializer();
serializer.Serialize(output, data);
yaml = output.ToString();
}
string yaml = yaml.Replace(">", "");
return yaml.Replace(Environment.NewLine + Environment.NewLine, Environment.NewLine);
And then back by:
string binaryText = ((YamlScalarNode)data.Children[new YamlScalarNode(ValueKey)]).Value
String value = Convert.FromBase64String(binaryText);
I would like to replace my global string constants with a nested enum for the keys I'm using to access columns in a database.
The structure is as follows:
enum DatabaseKeys {
enum User: String {
case Table = "User"
case Username = "username"
...
}
...
}
Each table in the database is an inner enum, with the name of the table being the enum's title. The first case in each enum will be the name of the table, and the following cases are the columns in its table.
To use this, it's pretty simple:
myUser[DatabaseKeys.User.Username.rawValue] = "Johnny"
But I will be using these enums a lot. Having to append .rawValue to every instance will be a pain, and it's not as readable as I'd like it to be. How can I access the String value without having to use rawValue? It'd be great if I can do this:
myUser[DatabaseKeys.User.Username] = "Johnny"
Note that I'm using Swift 2. If there's an even better way to accomplish this I'd love to hear it!
While I didn't find a way to do this using the desired syntax with enums, this is possible using structs.
struct DatabaseKeys {
struct User {
static let identifier = "User"
static let Username = "username"
}
}
To use:
myUser[DatabaseKeys.User.Username] = "Johnny"
Apple uses structs like this for storyboard and row type identifiers in the WatchKit templates.
You can use CustomStringConvertible protocol for this.
From documentation,
String(instance) will work for an instance of any type, returning its
description if the instance happens to be CustomStringConvertible.
Using CustomStringConvertible as a generic constraint, or accessing a
conforming type's description directly, is therefore discouraged.
So, if you conform to this protocol and return your rawValue through the description method, you will be able to use String(Table.User) to get the value.
enum User: String, CustomStringConvertible {
case Table = "User"
case Username = "username"
var description: String {
return self.rawValue
}
}
var myUser = [String: String]()
myUser[String(DatabaseKeys.User.Username)] = "Johnny"
print(myUser) // ["username": "Johnny"]
You can use callAsFunction (New in Swift 5.2) on your enum that conforms to String.
enum KeychainKey: String {
case userId
case email
}
func callAsFunction() -> String {
return self.rawValue
}
usage:
KeychainKey.userId()
You can do this with custom class:
enum Names: String {
case something, thing
}
class CustomData {
subscript(key: Names) -> Any? {
get {
return self.customData[key.rawValue]
}
set(newValue) {
self.customData[key.rawValue] = newValue
}
}
private var customData = [String: Any]()
}
...
let cData = CustomData()
cData[Names.thing] = 56
Edit:
I found an another solution, that working with Swift 3:
enum CustomKey: String {
case one, two, three
}
extension Dictionary where Key: ExpressibleByStringLiteral {
subscript(key: CustomKey) -> Value? {
get {
return self[key.rawValue as! Key]
}
set {
self[key.rawValue as! Key] = newValue
}
}
}
var dict: [String: Any] = [:]
dict[CustomKey.one] = 1
dict["two"] = true
dict[.three] = 3
print(dict["one"]!)
print(dict[CustomKey.two]!)
print(dict[.three]!)
If you are able to use User as dictionary key instead of String (User is Hashable by default) it would be a solution.
If not you should use yours with a nested struct and static variables/constants.
I want to make an Int from an String, but can't find how to.
This is my func:
func setAttributesFromDictionary(aDictionary: Dictionary<String, String>) {
self.appId = aDictionary["id"].toInt()
self.title = aDictionary["title"] as String
self.developer = aDictionary["developer"] as String
self.imageUrl = aDictionary["imageUrl"] as String
self.url = aDictionary["url"] as String
self.content = aDictionary["content"] as String
}
When using toInt() I get the error messag Could not find member 'toInt'. I can't use Int(aDictionary["id"]) either.
Subscripting a dictionary, with the dict[key] method, always returns an optional. For example, if your dictionary is Dictionary<String,String> then subscript will return an object with type String?. Thus the error that you are seeing of "Could not find member 'toInt()'" occurs because String?, an optional, does not support toInt(). But, String does.
You may also note that toInt() returns Int?, an optional.
The recommended approach to your need is something along the lines of:
func setAttributesFromDictionary(aDictionary: Dictionary<String, String>) {
if let value = aDictionary["id"]?.toInt() {
self.appId = value
}
// ...
}
The assignment will occur iff aDictionary has an id mapping and its value is convertible to an Int.
In action:
I'm using Reflection to get all the fields of my class in c#, but now I want to get the GC Generation of each variable in my class. How can I do this?
CSkyclass
{
float time = 0;
}
Sky = new CSkyclass();
void GetGeneration()
{
FieldInfo[] FieldArray = typeof(CSkyclass).GetFields(flags);
foreach(System.Reflection.FieldInfo Field in FieldArray)
{
string name = Field.Name; //"time"
int g = GC.GetGeneration(name); //should = GC.GetGeneration(Sky.time);
}
}
Is this even possible?
Thanks
You're trying to get the generation of the field's value:
GC.GetGeneration(field.GetValue(someInstance));