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Reflection for composite property names

I have a Dictionary<string, object> which holds a property name as string and it's value as object. I also have a Bind method extension which, through reflection, sets that propery name with its corresponding value:
public static T Bind<T>(this T #this,
Dictionary<string, object> newValues,
params string[] exceptions) where T : class
{
var sourceType = #this.GetType();
foreach (var pair in newValues.Where(v => !exceptions.Contains(v.Key)))
{
var property = sourceType.GetProperty(pair.Key,
BindingFlags.SetProperty |
BindingFlags.Public |
BindingFlags.Instance);
var propType = Nullable.GetUnderlyingType(property.PropertyType) ??
property.PropertyType;
property.SetValue(#this, (pair.Value == null) ? null :
Convert.ChangeType(pair.Value, propType), null);
}
return #this;
}
For instance, consider a class like this:
public class User
{
public string Name { get; set; }
public DateTime Date { get; set; }
}
Everything runs fine, except when I got a class with a property name of another object, like this:
public class User
{
public string Name { get; set; }
public DateTime Date { get; set; }
public Address Address { get; set; }
}
public class Address
{
public string PostalCode { get; set; }
}
So, if I try to send a Name property name, ok, but I got problems with composite property names, like Address.PostalCode.
Can you advise a way to handle that situation?
EDIT #1:
To summarize the problem: calling sourceType.GetProperty("Name", ...) in the context of a User class instance correctly allows to set its value, but it doesn't work using a sourceType.GetProperty("Address.PostalCode", ...) in same instance.
EDIT #2:
A more complete example should be:
var user = new User{ Address = new Address() };
var values = new Dictionary<string, object>
{
{ "Name" , "Sample" },
{ "Date" , DateTime.Today },
{ "Address.PostalCode", "12345" } // Here lies the problem
}
user.Bind(values);

My guess is that Convert.ChangeType only works for objects implementing IConvertible. Thus, I'd just add a check, and only use Convert.ChangeType if pair.Value has a type that implements IConvertible. Furthermore, afaik Convert does not use overloaded conversion operators, so you can save this check whenever pair.Value is not a struct, i.e.
object value;
if (pair.Value == null) {
value = null;
} else {
value = pair.Value.GetType().IsStruct ? Convert.ChangeType(pair.Value, propType) : pair.Value;
}
...

There are many binding engines out there, WPF, ASP.NET MVC, winforms in the core .NET and who knows how many others, you can check out all their source codes and documentation about their syntax.
Let's see the most simple case. Let's say that the variable X holds an object and you have the binding expression "A.B.C". Let's split up the binding path, the first part is "A". So you use reflection to get the property named "A" in X, and you put that other object into X. Now comes the second part, "B", so let's find a property named "B" in (the new) X. You find that, and put that into X. Now you get to the final part, "C", and now you can either read or write that property in X. The point is that you don't need recursion or anything, it's just a simple loop, you iterate over the parts of the binding expression, evaluate them, and you keep the current object in the same variable.
But the fact is that it can get much more complex than that. You could ask for array indexing, like "A.B[2].C". Or what if you have a path "A.B", and X.A is null, what do you do? Instantiate X.A, but what if it lacks a public parameterless constructor?
I want you to see that it can be a very complex problem. You have to specify a syntax and rules, and then implement that. You didn't specify in your question the exact syntax and rules you want to use. And if it happens to be more than the simple case I mentioned above, then the solution could be too lengthy.

I was able to solve it identifying if the property name have a period and recurring it:
public static T Bind<T>(this T #this,
Dictionary<string, object> newValues,
params string[] exceptions) where T : class
{
var sourceType = #this.GetType();
var binding = BindingFlags.Public | BindingFlags.Instance;
foreach (var pair in newValues.Where(v => !exceptions.Contains(v.Key)))
{
if(pair.Key.Contains("."))
{
var property = sourceType.GetProperty(
pair.Key.Split('.').First(),
binding | BindingFlags.GetProperty);
var value = property.GetValue(#this, null);
value.Bind(new Dictionary<string, object>
{
{
String.Join(".", pair.Key.Split('.').Skip(1).ToArray()),
pair.Value
}
});
}
else
{
var property = sourceType.GetProperty(pair.Key,
binding | BindingFlags.SetProperty);
var propType = Nullable.GetUnderlyingType(property.PropertyType) ??
property.PropertyType;
property.SetValue(#this, (pair.Value == null) ? null :
Convert.ChangeType(pair.Value, propType), null);
}
}
return #this;
}
Usage:
var user = new User {Address = new Address{ User = new User() }};
var values = new Dictionary<string, object>()
{
{"Name", "Sample"},
{"Date", DateTime.Today},
{"Address.PostalCode", "12345"},
{"Address.User.Name", "Sub Sample"}
};
user.Bind(values);
public class User
{
public string Name { get; set; }
public DateTime Date { get; set; }
public Address Address { get; set; }
}
public class Address
{
public string PostalCode { get; set; }
public User User { get; set; }
}

Pass Property to the Method in C#

I need to pass selection of properties of some types(one type each time), assume this is my type:
public class Product {
[PrimaryKey]
public long Id { get; set; }
[DisplayName("Name")]
public string Title { get; set; }
[Foreignkey(Schema = "Products", Table = "MajorCategory", Column = "Id")]
[DisplayName("MCat")]
public string MajorCategory { get; set; }
[Foreignkey(Schema = "Products", Table = "Category", Column = "Id")]
[DisplayName("Cat")]
public string Category { get; set; }
public long CategoryId { get; set; }
[BoolAsRadio()]
public bool IsScanAllowed { get; set; }
}
So I need a way to pass the list of properties of this type to other Type(Target Type), and use property name, and attributes, and I don't need values, something like the following Pseudo-code:
List<Property> propertyList = new List<Property>();
propertyList.Add(Product.Id);
PropertyList.Add(Product.Title);
TargetType target = new TargetType();
target.Properties = propertyList;
public class TargetType {
public List<Property> Properties { get; set;}
GetAttributes() {
foreach(Property item in Properties){
Console.WriteLine(item.Name)
//Get Attributes
}
}
}
Is there any way to pass just like Product.Id and use name and attributes of that? I don't sure but maybe PropertyInfo can help, I think just can pass List of Object but in that case I can't use attributes and names, what is your suggestion to handle this? or something like this? if I am wrong at all so how can I implement it?

Funny, I was just answering a similar question, or at least I think it is.
It looks like you're trying to concatenate the properties of two types into one? You need an ExpandoObject:
http://msdn.microsoft.com/en-us/library/system.dynamic.expandoobject%28v=vs.100%29.aspx
For an implementation of a nested merge, see this:
C# deep/nested/recursive merge of dynamic/expando objects
Basically, you want a keyed list of properties, to start from. The following code will do that for any .NET object:
var props = object.GetType().GetProperties().ToDictionary<PropertyInfo, string>(prop => prop.Name);
And after that it depends on what precisely it is you want to achieve - a true copy of the object, merge with another, or just maintaining the list.

You can make use of reflection in .NET here:
List<PropertyInfo> propertyList = new List<PropertyInfo>();
Type productType = typeof (Product);
propertyList.Add(productType.GetProperty("Id"));
propertyList.Add(productType.GetProperty("Title"));
TargetType target = new TargetType();
target.Properties = propertyList;
public class TargetType {
public List<PropertyInfo> Properties { get; set;}
List<object> GetAttributes()
{
List<object> attributes = new List<object>();
foreach(PropertyInfo item in Properties)
{
Console.WriteLine(item.Name);
attributes.AddRange(item.GetCustomAttributes(true));
}
return attributes;
}
}

You can use a list of PropertyInfo, List<PropertyInfo> as the type of your TargetType .Properties. To get the properties you can try it like this using Reflection.
targetType.Properties = product.GetType().GetProperties().ToList();

You can build list of properties using expression trees, e.g. you can make something like this:
var propertiesListBuilder = new PropertiesListBuilder<Product>();
propertiesListBuilder
.AddProperty(_ => _.Id)
.AddProperty(_ => _.Title);
var target = new TargetType();
target.Properties = propertiesListBuilder.Properties;
The only concern here is performance, i.e. it might be not good idea to recreate such property lists over and over again, most probably they should be cached. At the same time you'll get intellisense, compiler checks and refactoring support for your property lists.
Below is a sample implementation of this stuff.
static class PropertyInfoProvider<T>
{
public static PropertyInfo GetPropertyInfo<TProperty>(Expression<Func<T, TProperty>> expression)
{
var memberExpression = (MemberExpression)expression.Body;
return (PropertyInfo)memberExpression.Member;
}
}
class PropertiesListBuilder<T>
{
public IEnumerable<PropertyInfo> Properties
{
get
{
return this.properties;
}
}
public PropertiesListBuilder<T> AddProperty<TProperty>(
Expression<Func<T, TProperty>> expression)
{
var info = PropertyInfoProvider<T>.GetPropertyInfo(expression);
this.properties.Add(info);
return this;
}
private List<PropertyInfo> properties = new List<PropertyInfo>();
}

typeof(Product).GetProperties() would give you all (public) properties as PropertyInfo[].
See also MSDN.

DataBinding: 'System.Web.UI.Pair' does not contain a property with the name 'First'

I'm data binding a list of pairs to a drop down list, for some reason it's not working and I'm intrigued.
The code I am using is :
public void BindDropDown(List<Pair> dataList)
{
ddlGraphType.DataTextField = "First";
ddlGraphType.DataValueField = "Second";
ddlGraphType.DataSource = dataList;
ddlGraphType.DataBind();
}
I'm getting this exception, which is a lie!
DataBinding: 'System.Web.UI.Pair' does not contain a property with the name 'First'.
Thanks in advance.
Added
I know what the exception means, but a pair object does contain the First and Second properties, that's where the problem lies.

First and Second are Fields not properties of Pair type. You need to create a class with two properties:
public class NewPair
{
public string First { get; set; }
public string Second { get; set; }
}
EDIT: Use of Tuple : suggested by #Damien_The_Unbeliever & #Chris Chilvers
List<Tuple<string, string>> list = new List<Tuple<string, string>>()
{
new Tuple<string,string>("One","1"),
new Tuple<string,string>("Two","2"),
};
ddlGraphType.DataTextField = "Item1";
ddlGraphType.DataValueField = "Item2";
ddlGraphType.DataSource = list;
ddlGraphType.DataBind();

Theat means the target property must be a dependency property. This also means that you cannot bind a field and Pair.First is field not property

public sealed class Pair
{
}
Fields:
Public field First Gets or sets the first object of the object pair.
Public field Second Gets or sets the second object of the object pair.
See MSDN.

Probably you've forgot the {get; set;} after declaring the properties.
public class A
{
//This is not a property
public string Str;
//This is a property
public string Str2 {get; set;}
}

C# Accessing object properties indexer style

Is there any tool,library that would allow me to access my objects properties indexer style ?
public class User
{
public string Name {get;set;}
}
User user = new User();
user.Name = "John";
string name = user["Name"];
Maybe the dynamic key word could help me here ?

You can use reflection to get property value by its name
PropertyInfo info = user.GetType().GetProperty("Name");
string name = (string)info.GetValue(user, null);
And if you want to use index for this you can try something like that
public object this[string key]
{
get
{
PropertyInfo info = this.GetType().GetProperty(key);
if(info == null)
return null
return info.GetValue(this, null);
}
set
{
PropertyInfo info = this.GetType().GetProperty(key);
if(info != null)
info.SetValue(this,value,null);
}
}

Check out this about indexers. The dictionary stores all the values and keys instead of using properties. This way you can add new properties at runtime without losing performance
public class User
{
Dictionary<string, string> Values = new Dictionary<string, string>();
public string this[string key]
{
get
{
return Values[key];
}
set
{
Values[key] = value;
}
}
}

You could certainly inherit DynamicObject and do it that way.
http://msdn.microsoft.com/en-us/library/system.dynamic.dynamicobject.trygetindex.aspx
Using the simple indexer method mentioned here by others would limit you to either returning only 'object' (and having to cast) or having only string types in your class.
Edit: As mentioned elsewhere, even with dynamic, you still need to use either reflection or some form of lookup to retrieve the value inside the TryGetIndex function.

You cannot do this until the class implements a Indexer.

If you just want to access a property based on a string value you could use reflection to do something similar:
string name = typeof(User).GetProperty("Name").GetValue(user,null).ToString();

You could build it yourself with reflection and indexer.
But for what do you need such a solution?

Accessing C# property name or attributes

I would like to automatically generate SQL statements from a class instance. The method should look like Update(object[] Properties, object PrimaryKeyProperty). The method is part of an instance (class, base method - generic for any child). Array of properties is an array of class properties, that will be used in update statement. Property names are equal to table field names.
The problem is that I can't get property names.
Is there any option to get a property name inside class instance?
sample:
public class MyClass {
public int iMyProperty { get; set; }
public string cMyProperty2 { get; set; }
{
main() {
MyClass _main = new MyClass();
_main.iMyProperty.*PropertyName* // should return string "iMyProperty"
{
I am aware of PropertyInfo, but I don't know hot to get the ID of a property from GetProperties() array.
Any suggestion?

Just wrote an implementation of this for a presentation on lambdas for our usergroup last Tuesday.
You can do
MembersOf<Animal>.GetName(x => x.Status)
Or
var a = new Animal()
a.MemberName(x => x.Status)
the code:
public static class MembersOf<T> {
public static string GetName<R>(Expression<Func<T,R>> expr) {
var node = expr.Body as MemberExpression;
if (object.ReferenceEquals(null, node))
throw new InvalidOperationException("Expression must be of member access");
return node.Member.Name;
}
}
Link to the presentation and code samples.
Also in SVN (more likely to be updated): http://gim-projects.googlecode.com/svn/presentations/CantDanceTheLambda

I found a perfect solution in This Post
public static string GetPropertyName<T>(Expression<Func<T>> propertyExpression)
{
return (propertyExpression.Body as MemberExpression).Member.Name;
}
And then for the usage :
var propertyName = GetPropertyName(
() => myObject.AProperty); // returns "AProperty"
Works like a charm

You can do something like this:
Type t = someInstance.getType();
foreach (MemberInfo mi in t.GetMembers())
{
if (mi.MemberType == MemberTypes.Property)
{
Console.WriteLine(mi.Name);
}
}
to get all the property names for instance's type.

You can get the name (I assume that's what you meant by ID) of a property using PropertyInfo.Name. Just loop through the PropertyInfo[] returned from typeof(className).GetProperties()
foreach (PropertyInfo info in typeof(MyClass).GetProperties())
{
string name = info.Name;
// use name here
}

Since you already have an explicit handle to the specific property you want, you know the name - can you just type it?

Not 100% sure if this will get you what you're looking for, this will fetch all properties with [Column] attribute inside your class:
In the datacontext I have:
public ReadOnlyCollection<MetaDataMember> ColumnNames<TEntity>( )
{
return this.Mapping.MappingSource.GetModel(typeof(DataContext)).GetMetaType(typeof(TEntity)).DataMembers;
}
Fetching the table column-names that are properties inside the class:
MyDataContext db = GetDataContext();
var allColumnPropertyNames = db.ColumnNames<Animal>().Where(n => n.Member.GetCustomAttributes(typeof(System.Data.Linq.Mapping.ColumnAttribute), false).FirstOrDefault() != null).Select(n => n.Name);

Let's say (from the first sample, method update of a class MyClass):
public class MyClass {
public int iMyStatusProperty { get; set; }
public int iMyKey { get; set; }
public int UpdateStatusProperty(int iValue){
this.iMyStatusProperty = iValue;
return _Update( new[iMyStatusProperty ], iMyKey); // this should generate SQL: "UPDATE MyClass set iMyStatusProperty = {iMyStatusProperty} where iMyKey = {iMyKey}"
}
{iMyStatusProperty} and {iMyKey} are property values of a class instance.
So, the problem is how to get property name (reflection) from a property without using names of properties as strings (to avoid field name typos).