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Replace template Placeholder with Object Properties with Reflection

In C#, I want to replace the string Placeholder with Object Properties using Reflection
string formula = "{\"Name\": \"{{Name}}\", \"Email\": \"{{Email}}\" }";
Student student = new Student();
student.Name = "Parker";
student.Email = "Parker#xyz.com";
student.Address = "Mark Avenue";
var result1 = GenerateJson(formula, student);
//Output : "{\"Name\": \"Parker\", \"Email\": \"Parker#xyz.com\" }"
student.Name = "Royal";
student.Email = "Royal#xyz.com";
student.Address = "Cross Lane";
var result2 = GenerateJson(formula, student);
//Output : "{\"Name\": \"Royal\", \"Email\": \"Royal#xyz.com\" }"
public string GenerateJson(string formula, Student student)
{
string result = "";
//logic for replacing the Placeholder woth object properties
return result;
}
class Student
{
public string Name { get; set; }
public string Email { get; set; }
public string Address { get; set; }
}

If you really don't want or cannot use Json.NET than you can try solution below
public string GenerateJson(string formula, Student student)
{
return Regex.Replace(formula, #"\{\{(\w+)\}\}", match => typeof(Student).GetProperty(
match.Groups[1].ToString())?.GetValue(student)?.ToString());
}

You can deserialize it to ExpandoObject (IDictionary<string,object>). Then compare property names with the known type. If there is match between Dictionary's key and student's propertyName. Replace ExpandoObject's Value with Student's property's value. After all, serialize it to json.
Here it is,
public string GenerateJson(string formula, Student student)
{
IDictionary<string, object> templateValues = JsonConvert.DeserializeObject<IDictionary<string, object>>(formula);
PropertyInfo[] sourceProperty = typeof(Student).GetProperties();
foreach (var item in sourceProperty)
{
KeyValuePair<string,object> value = templateValues.FirstOrDefault(x=> x.Key == item.Name);
if (value.Key != null)
{
templateValues[item.Name] = item.GetValue(student);
}
}
return JsonConvert.SerializeObject(templateValues);
}

It looks like the actual problem is retrieving the value of specific properties to generate an API signature. It's unclear if the signature to sign really needs to be a JSON string or not.
The easiest way is to create an anonymous type with the necessary properties and serialize it, eg :
var payload=JsonConvert.Serialize(new {student.Name,student.Email});
This is far faster than any reflection code and allocates a single extra object only. If you want to use an API with a lot of different request types, it pays to use a code generator or in C# 9, a source generator to generate such calls.
It's possible (but slow) to use reflection to retrieve specific properties, eg with :
var dict=typeof(Student).GetProperties()
.Where(prop=>myProps.Contains(prop.Name))
.ToDictionary(prop=>prop.Name,prop=>prop.GetValue(student));
var json=JsonConvert.Serialize(dict);
A JSON object is actually a dictionary, so serializing a dictionary behaves similarly to serializing an object with the same properties.
Reflection is relatively expensive though, so it's a good idea to cache the PropertyInfo objects you want and reuse them:
Dictionary<Type,PropertyInfo[]> _properties=new Dictionary<Type,PropertyInfo[]>();
...
string GenerateJson<T>(T item)
{
PropertyInfo[] props;
if (!_properties.TryGetValue(typeof(T),out props))
{
props=typeof(Student).GetProperties()
.Where(prop=>myProps.Contains(prop.Name))
.ToArray();
}
var dict=props.ToDictionary(prop=>prop.Name,prop=>prop.GetValue(item));
return JsonConvert.Serialize(dict);
}

Linq to sql .Dynamic Where: string with System.Linq.Dynamic.ParseException: No property or field '0' exists in type 'myTable'

I'm trying to do a dynamic query to one of myTables
For that I'm usin the following function:
public async Task<bool> search(DBContext db, M model, string uniqueNonIDField)
{
Type modelType = model.GetType();//get model of generic
object modelInstance = Activator.CreateInstance(modelType);
PropertyInfo field = modelType.GetProperty(uniqueNonIDField); //get property to get existing value
if (field == null)
throw new Exception(string.Format("Campo {0} Não encontrado", uniqueNonIDField));
string value = (string)field.GetValue(model, null); //get value to search in myTable
field.SetValue(model, Regex.Replace(value, #"[\u002D\u2010\u2012\u2013\u2014]", "-"), null); //do some clean up
value = (string)field.GetValue(model, null); //get new value after being cleaned
if (db.Set(modelType).Where(String.Format("#0=#1", uniqueNonIDField, value)).Count() == 0) //Test if there is already any object in myTable with that value.
{...do stuff}
...
}
But there is an error:
System.Linq.Dynamic.ParseException: No property or field '0' exists in type 'myTable'
If I hardcode all expression like:
if (db.myTable.Where("existingField=123").Count() == 0){...}
the error persist with:
System.Linq.Dynamic.ParseException: No property or field '123' exists in type 'myTable'
I'm trying to do as exemplified in many examples and saw many other stackoverflow similar answers, but can't find the reason for the error. Rookie mistake probably.
Can you please help me finding it?

You can pass a string to the where statement. System.Linq.Dynamic allows you to filter by string.
Everything seems to be okay in your code and maybe your issue is related to this one:
https://github.com/zzzprojects/System.Linq.Dynamic/issues/101
Are you using this code under dotnetcore? If yes then please install the related NuGet package and change the using to System.Linq.Dynamic.Core

You cannot pass your where statement as a string like this: Where("existingField=123"), you do it as an expression Expression<Func<TSource,bool>> predicate. In order to pass that expression you will have to know the type for which you want to filter
EDIT: Sample Where
Lets say you have MyClass in your DbContext like this:
public class MyClass
{
public int Id { get; set; }
public string Name { get; set; }
}
public class MyContext : DbContext
{
public DbSet<MyClass> MyClass { get; set; }
}
Then to filter on the Name or Id property of MyClass, all you do is:
var filteredEntities = dbContext.MyClass.Where(x => x.Name == "test").ToList();

How to retrieve object properties with LINQ?

Let's say I have this object:
public class Foo
{
public string FirstProp {get;set;}
public string SecondProp {get;set;}
public string ThirdProp {get;set;}
}
Now I would like to retrieve only the FirstProp and the SecondProp from that object and concat all the property values into one string.
I have one solution in mind which would't be clean imo. Here it is:
var foo = new Foo("test1","test2","test3");
var propertyNames = new[] {"FirstProp", "SecondProp"};
var properties = foo.GetType().GetProperties().Where(x => propertyNames.Contains(x.Name));
//Then loop through each retrieved property and concat the string
So basically I am just looking for a cleaner solution where I wouldn't be dependent on an array of string.

var foo = new Foo(...);
var result = string.Join(",", new[]{ foo.FirstProp, foo.SecondProp });
Does this suffice? Or do you need Reflection for dynamic typing? If so, one can also supply MemberExpressions to dynamically get the values. Are you dealing with a collection of instances? Do you need this functionality extracted in a helper-method with a parameter for the needed properties?

Can't return specific nested class property

I made a class for deserialize a JSON (I'm using JSON.net), this is the structure:
public class User
{
public string Name { get; set; }
public string Surname { get; set;}
}
public class RootObject
{
public List<User> Users { get; set; }
}
I deserialize the JSON like this:
var obj = JsonConvert.DeserializeObject<RootObject>(responseText);
Now If I want return all the JSON I simply do: return obj.Users; but how can I return a specific property of the class User? In particular the Name property. I tried this:
return obj.Users.name // user list does not contain any name property
Also I tried with LINQ:
obj.Select(c => c.Name).Single();
But I can't use Select because I need to declare obj as:
var obj = JsonConvert.DeserializeObject<List<RootObject>>(responseText);
If instead I return obj.user; I can use LINQ and access to the name. But how can do this in the method that return the response?

Add a reference to class
using System.Linq;
since user is of type List you can apply lambda expression in it. Do not use Single it will fail if user will have more than one record in it, use FirstOrDefault instead. It will work for zero or more number of elements
var obj = JsonConvert.DeserializeObject<RootObject>(responseText);
string name = obj.user.Select(p=> p.name).FirstOrDefault();
string surname = obj.user.Select(p=> p.surname).FirstOrDefault();

You have to use one user instead of the whole list as RootObject.user is a List<User> and not an instance of User:
var name = obj[0].Name;
Or whatever element within your list you want to use.
Alternativly use LINQ:
var user = obj.FirstOrDefault();
if (user != null) name = user.name;

HowTo use Dynamic linq with an index instead of a property name

I have an ICollection with objects:
private ObservableCollection<ViewItem> items;
The viewItems have no properties. The data will be accessed via an index with
public object this[int index] {
get{ .... }
set {....}
}
I have a geneal class for filtering. The linq with properies will work fine. I use (the important code only):
Queryable = CreateQueryable((IEnumerable<object>)mItemsSource.SourceCollection, ItemType);
mQuery = Queryable.Where(filterString).Cast<object>();
ilteredCollection = mQuery.ToList();
with:
private static IQueryable CreateQueryable(IEnumerable<object> collection, Type itemType)
{
if (itemType == null) return null;
var queryableList = collection.AsQueryable();
return queryableList.Provider.CreateQuery(
Expression.Call(
typeof(Queryable), "Cast",
new Type[] { itemType },
queryableList.Expression));
}
So I can use a filter string like: Id>10 or Name="abc"
where Id and Name are property names.
But I have also Object in another collection which only have access via index. so I have an where string like:
[0]>10 or [1]="abc"
I didn't find any solution. The only hint I could find is to use:
new(it([idx] as Type)
where idx is element index and Type is a type of this element
e.g.
[0]>10 --> new(it[0] as object)>10
But than I get the error:
{"Operator '=' incompatible with operand types 'DynamicClass1' and 'Int32'"}
Useing a string in my filter like:
new(it[0] as object)>"10"
than the error is:
{"Operator '=' incompatible with operand types 'DynamicClass1' and 'string'"}
So - how can I solve this problem. Because this is a general Filterclass I also don't know the type. So in the as statement I can only use object or something like this.
I hope anyone can help me. Perhaps the dynamic keyword of C# 4.0 will help??
BTW a workaround will be to impement a wrapper in each class with indexer, but this will be a lot of stupid work. And that is something a real programmer don't like ;). I am sure there is a solution!

Cheer up !!
First of all -- How to access Current Instance ?
When parsing a lambda expression with a single unnamed parameter, the members of the unnamed parameter are automatically in scope in the expression string, and the current instance given by the unnamed parameter can be referenced in whole using the keyword it. For example,
customers.Where("Country = #0", country);
is equivalent to
customers.Where("it.Country = #0", country);
Above concept has been explained here.
From above explanation, we can now access the indexer property as it[#0] where #0 is value of index to be passed, as explained below.
//Consider below class
public class Product
{
private NameValueCollection collection = new NameValueCollection();
public string Company { get; set; }
public string Distributor { get; set; }
public int ID { get; set; }
...
public string this[string index]
{
get { return collection[index]; }
set { if(!string.IsNullOrEmpty(value)) collection[index]=value; }
}
}
//Main Code
List<Product> list = new List<Product>();
Product product = new Product() { Company = "Nestle", Distributor = "xyz", ID = 1 };
product["Name"] = "Maggi";
list.Add(product);
var filteredList = list.AsQueryable().Where("it[#0]=#1", "Name", "Maggi"); //Accessing the current item by indexer property
foreach (Product productItem in filteredList)
{
Console.WriteLine(productItem.Company);
}
Hope this helps you !! :)

Your usage of new keyword is wrong.
It does not cast object (nor does as).
Keyword new is used to create new object of anonymous class with the specified properties.
Thus new(it[idx] as Type) will create new object with property Type having the value it[idx]. It is equivalent to C#'s: new { Type = this[idx] }.
As I have already pointed out in Dynamic linq: Is there a way to access object data by index?, you need to cast it in the following manner: Int32(it[0]) > 10 for your pseudo-query [0] > 10.