Linq Join on Like%

One of the recent requirements I came across recently needed what looks like a Join on a ‘Like%’. Let me cite an example to demonstrate the requirement.
Consider the Collections below.

Master Collection

ID Name
1 Jia Anu
2 Sreena Anu
3 Anu Viswan

Child Collection

ID First Name Age
1 Jia 2
3 Sreena 34
5 Anu 35

I would like to Join on Master.Name and Child.FirstName where Child.FirstName StartsWith Master.Name. The expected output is as follows.

Name FirstName Age
Jia Anu Jia 2
Sreena Anu Sreena 34
Anu Viswan Anu 35

Let’s begin by defining the input collections.

var master = new List<Master>
{
new Master{Id=1,Name="Jia Anu"},
new Master{Id=2,Name="Sreena Anu"},
new Master{Id=3,Name="Anu Viswan"}
};

var child = new List<Child>
{
new Child{Id=1,FirstName="Jia",Age=2},
new Child{Id=2,FirstName="Sreena",Age=34},
new Child{Id=3,FirstName="Anu",Age=35}
};

Where Master and Child is defined as

public class Master
{
public int Id {get;set;}
public string Name {get;set;}
}

public class Child
{
public int Id{get;set;}
public string FirstName {get;set;}
public int Age {get;set;}
}

The default Join uses Equality as Comparer, and is not useful for us in this scenario. The solution lies in a little known overload of Group, which allows to provide our own customer Comparer. Let’s define our Custom Comparer.

class StartsWithEqualityComparer: IEqualityComparer<string>
{
public bool Equals(string right, string left)
{
return left.StartsWith(right);
}
public int GetHashCode(string obj) { return 0; }
}

Now, we can use our StartsWithEqualityComparer.

var result = master.Join(child,
m=>m.Name,
c=>c.FirstName,
(m,c)=> new
{
Name = m.Name,FirstName = c.FirstName,Age = c.Age
}
},new StartsWithEqualityComparer());

That’s it, we have our GroupBy with Like%.

Caliburn.Micro #008: Gesture Recognition using Short-Hand Syntax

In this part of Caliburn.Micro tutorials we would explore how to configure and use Gesture Recognition with Caliburn.Micro, particularly exploiting the Short-Hand syntax for Actions. Caliburn.Micro doesn’t support this out of the box, so obviously we need to work around the Actions to provide support for Gestures. Let’s first formulate the syntax of how we would like to add a Gesture and its binding in XAML and then find our way to it.

We would ideally like to use a syntax, that is close to Action Syntax for triggering events.

[Event Click]=[Action Method1] // Normal Events
[Key F12]=[Action Method1] // Ideal Gesture Syntax.

The first step required would be to write a Trigger that would catch the KeyPress event. The trigger should provide ability to pass the expected “Key” and invoke the binded action when the expected “Key” is pressed. Let’s go ahead and write the required Custom Trigger.

public class KeyTrigger : TriggerBase<UIElement>
{
public static readonly DependencyProperty KeyProperty =
DependencyProperty.Register("Key", typeof(Key), typeof(KeyTrigger), null);

public Key Key
{
get => (Key)GetValue(KeyProperty);
set => SetValue(KeyProperty, value);
}

protected override void OnAttached()
{
base.OnAttached();
AssociatedObject.KeyDown += OnAssociatedObjectKeyDown;
}

protected override void OnDetaching()
{
base.OnDetaching();
AssociatedObject.KeyDown -= OnAssociatedObjectKeyDown;
}

private void OnAssociatedObjectKeyDown(object sender, KeyEventArgs e)
{
if (e.Key == Key)
{
InvokeActions(e);
}
}
}

The KeyTrigger is quite self-explainatory. It declares Dependency Property called “Key” of System.Windows.Input.Key, and verifies if the Key Pressed is actually the one registered in KeyDown Event of AssociatedObject. If the Key matches the registered Key, it invokes the associated Action.

The Step is to Write our Custom Action Format, that would be recognized by the Caliburn.Micro Parser, and calls from Trigger(and there by Action). In order to achieve this, we re-define Parser.CreateTrigger method, which is responsible to generate the trigger. We do this in our Bootstrapper, overriding Configure Method.

// In Bootstrapper

protected override void Configure()
{
var defaultCreateTrigger = Parser.CreateTrigger;

Parser.CreateTrigger = (target, triggerText) =>
{
if (string.IsNullOrEmpty(triggerText)) return defaultCreateTrigger(target, null);

var regex = new Regex($@"^\[(?<{X_ACTION}>[a-zA-Z]+)\s(?<{X_SHORTCUT}>[a-zA-Z0-9]+)\]$");
var matches = regex.Match(triggerText.Trim());

switch (matches.Groups[X_ACTION].Value.ToUpper())
{
case X_KEY:
return new KeyTrigger
{
Key = (Key)Enum.Parse(typeof(Key), matches.Groups[X_SHORTCUT].Value, true),
};
default:
return defaultCreateTrigger(target, triggerText); ;
}
};
}

As observed, we check if the triggerText contains our special keywords, and if so, create our Custom trigger, namely KeyTrigger. In all other case, it returns the default trigger.

That’s all we require to configure our Gesture Recognition. We can now move on to our View and define the Gesture using our custom Action syntax.

cal:Message.Attach="[Key Enter] = [Action Increment]"

You can access the complete code sample, demonstrated in this post in my Github.

Btw, Merry Christmas !!!

Filter List and Display Type members with specified attribute

One of the recent questions that was intriguing (for me) in Stackoverflow was the need to Process a List and while displaying the result, display only the properties that are decorated with a specific attribute.

Let me explain with an example. Consider the following Entity.

public class Employee
{
public int ID { get; set; }

public string Place { get; set; }

[IncludeinReport]
public string BusinessVertical { get; set; }

[IncludeinReport]
public string Region { get; set; }

public string Country { get; set; }

[IncludeinReport]
public string BusinessUnit { get; set; }
}

For a List<Employee>, the expected result would display only “BusinessVertical”, “Region”, and “BusinessUnit” in the result. Let’s begin by creating a mock sample data to test it.

var list = new List<Employee>
{
new Employee{ID = 1, Region = "Europe", BusinessUnit="Software", BusinessVertical = "Sample1"},
new Employee{ID = 1, Region = "Asia", BusinessUnit="Software", BusinessVertical = "Sample1"},
new Employee{ID = 1, Region = "Asia", BusinessUnit="Hardware", BusinessVertical = "Sample1"},
new Employee{ID = 1, Region = "Europe", BusinessUnit="Software", BusinessVertical = "Sample1"},
new Employee{ID = 1, Region = "Asia", BusinessUnit="Telecom", BusinessVertical = "Sample1"},
new Employee{ID = 1, Region = "Europe", BusinessUnit="Software", BusinessVertical = "Sample1"},
};

Just to make things interesting, we would add restriction that the result needs to be Sorted By Region and Then by BusinessUnit. A LINQ solution would have been ideal, but unfortunately, I couldn’t go all the way with LINQ. But here is the solution I could suggest.
The first step, obviously was to get the List of Properties that has the required Attribute, which we can achieve using Reflection.

var properties = typeof(Employee).GetProperties().Where(prop => Attribute.IsDefined(prop, typeof(IncludeinReport))).Select(v=>v);
var intermediate = list.OrderBy(c => c.Region).ThenBy(x=>x.BusinessUnit).SelectMany((x,index)=> properties.Select(v=> new {GroupId = index, Dict = new KeyValuePair<string,object>(v.Name, v.GetValue(x))})) ;
var resultList = intermediate.GroupBy(x=>x.GroupId).Select(x=>x.ToList().Select(c=>c.Dict).CreateObject());

Where CreateObject is defined as

public static class Extensions
{
public static ExpandoObject CreateObject(this IEnumerable<KeyValuePair<string,object>> source)
{
dynamic returnValue = new ExpandoObject();
var dict = returnValue as IDictionary<string, object>;
foreach (var kvp in source)
{
dict.Add(kvp.Key, kvp.Value);
}
return returnValue;
}
}

Since even anonymous types needs to have Property Names defined in compile time, the only solution to create a Dynamic Type (including property names) was using ExpandoObject.
This would give you the desired output as enclosed in the screenshot.

Capture

Again, this is the solution I could arrive at, there would be better ones. I would certainly be interested to know a better solution. If anyone would like to follow the OP in question, please follow it StackoverFlow

Mapping XML Using Automapper

Automapper comes handy when you have to deal with a lot of DTOs, making it very easy to map one type to another. But there are situations where you might need an extra hand.

Consider the following Type definitions.

public class SourceUser
{
public string Name {get;set;}
public int Age {get;set;}
public string Address {get;set;}
}

public class DestinationUser
{
public string UserName{get;set;}
public int Age{get;set;}
public Address Address{get;set;}
}
public class Address
{
public string City {get;set;}
public string State {get;set;}
public string Country {get;set;}
}

The Source.Address is a XML representation of Address. Your requirement is to configure Automapper to convert SourceUser to DestinationUser. Let’s define an example SourceUser first, so that our demonstration could be easier.

var sourceUser = new SourceUser
{
Name = "Anu Viswan",
Age = 35,
Address = "<Address><County>India</Country><State>Kerala</State><City>Cochin</City></Address>"
};

This is where ConstructUsing method of comes into place. The first step is define our custom Construction Method.

static DestinationUser ConstructAddress(SourceUser src)
{
XDocument xdoc = new XDocument();
xdoc = XDocument.Parse(src.Address);
var destinationUser = new DestinationUser
{
Address = new Address
{
Country = xdoc.Root.Element(nameof(Address.Country)).Value,
City = xdoc.Root.Element(nameof(Address.City)).Value,
State = xdoc.Root.Element(nameof(Address.State)).Value,
}
};

return destinationUser;
}

With our Construction Method ready, we now move on to configure Automapper.

Mapper.Initialize(cfg =>
cfg.CreateMap<SourceUser, DestinationUser>()
.ConstructUsing(x => ConstructAddress(x))
.ForMember(dest => dest.UserName, source => source.MapFrom(s => s.Name))
.ForMember(dest => dest.Age, source => source.MapFrom(s => s.Age))
.ForMember(dest=> dest.Address, source => source.Ignore()));

Do note that we have relied on Automapper for rest of Properties, which can be easily mapped. It is also important to instruct Automapper to Ignore the Address property in its routine parsing. That would give you the desired result and you can map the incompatible Types using the following.

var destinationUser = Mapper.Map<DestinationUser>(sourceUser);

Json Recipes

Here are few quick recipes with Newtonsoft.Json

Recipe 01 : Convert Json to XML

One way to convert a Json to XML would be to convert Json to intermediate class structure and then serialize the class using XMLSerializer. But why go the long way when you can do it directly.

Let’s check the code straightaway.

var jsonString = @"{
'Family':[
{
'Name':'Anu',
'Age': '35'
},
{
'Name':'Jia',
'Age': '2'
}
]
}";
var xml = (XmlDocument)JsonConvert.DeserializeXmlNode(jsonString,"root");

That’s it, you have your XML. Output is shown below.

<root>
<Family>
<Name>Anu</Name>
<Age>35</Age>
</Family>
<Family>
<Name>Jia</Name>
<Age>2</Age>
</Family>
</root>

Recipe 02 : Convert XML to Json

No prizes for guess how to do it other way around (XML to Json) – Yes, you Serialize.

var xmlString = @"<root>
<Family>
<Name>Anu</Name>
<Age>35</Age>
</Family>
<Family>
<Name>Jia</Name>
<Age>2</Age>
</Family>
</root>";

XmlDocument doc = new XmlDocument();
doc.LoadXml(xmlString);
var json = JsonConvert.SerializeXmlNode(doc);

Recipe 03: Dynamic Json
Consider the following Json. What could be the best way to model it in C# class.

{
'Key1' : 'some value 1',
'Key2' : 'some value 1',
'Key3' : 'some value 1',
'Key4' : 'some value 1',
}

Where you do not know how many Keys would be there and what could be there name ? The easiest way would be if you can serialize it to an Dictionary. The ‘JsonExtensionData‘ attribute allows you to do exactly the same.

<br />public class JsonSample
{
[JsonExtensionData]
public Dictionary<string,object> RandomKeyValuePair {get;set;}
}

// Client Code
var jsonString = @"
{
'Key1' : 'some value 1',
'Key2' : 'some value 1',
'Key3' : 'some value 1',
'Key4' : 'some value 1',
}";

var jsonSampleObject = JsonConvert.DeserializeObject<JsonSample>(jsonString);

Of course the reverse is also possible.

var jsonResult = JsonConvert.SerializeObject(jsonSampleObject);

More recipes later.

Verifying if View Exists for specified ViewModel

There might raise situations in your Project where you might be interested to check if the ViewModel specified has a corresponding View defined and gradefully handle the error, than throwing an exception.

Caliburn Micro’s ViewLocator class provides you methods that enables you to do exactly that.

if ((ViewLocator.LocateForModelType(typeof(DummyViewModel), null, null) is TextBlock tb
&& tb.Text.StartsWith("Cannot find", StringComparison.InvariantCultureIgnoreCase)))
{
// View does not exist, Terminate or redirect to another
}
else
{
// View found, redirect to intended one
}