Anonymous LINQ + MVC Types

Question

I have seen many questions about this, but I have never had the answer I need.

I am converting a rather large web application from Web Forms to MVC, and after a while I ran into the problem of transferring data to a view. In action, I execute the code:

//This is just an example ViewData["QProducts"] = from p in db.Products select new{Name = p.Name, Date = p.ToShortDateString() } ViewData["QUsers"] = from u in db.Users select u;

I use a foreach loop to iterate over objects in html, for example:

 foreach(var q in (IEnumerable)ViewData["QEvents"]) { /*Print the data here*/ } 

Before using MVC, I just used asp:Repeater , but since it is MVC, I cannot use ASP.NET controls.

How should I pass this data to a view? I really have no way of not using Anonymous types here. <%#ViewData.Eval()%> will obviously not work.

Any ideas?

Answer 1

Instead of an anonymous type, create a type to store the name and date:

 public class NameDate { public string Name { get; set; } public DateTime Date { get; set; } } 

Then use this in your Linq query:

 from p in db.Products select new NameDate { Name = p.Name, Date = p.Date } 

Strictly enter your view as MyView<IEnumerable<NameDate>> , and then just do foreach ( var nameDate in ViewData.Model )...

Answer 2

If you feel a little lazy, you can use this code here ... It's a little longer, but basically it's a wrapper for Reflection ...

 var something = { Name = "Jim", Age = 25 }; AnonymousType type = AnonymousType.Create(something); //then used... string name = type.Get<string>("Name"); int age = type.Get<int>("Age", -1 /* optional default value */); 

And here is the code ...

 using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Reflection; namespace Code { /// <summary> /// A convenient method of accessing the values of an /// anonymous type without needing to define a separate class /// </summary> public class AnonymousType { #region Constants private const string EXCEPTION_MISSING_PARAMETER_INFORMATION = "Unable to match the parameter '{0}' to a property in the AnonymousType. This could be due to a casting problem or a Property that does not exist."; private const string EXCEPTION_COULD_NOT_ACCESS_FIELD = "Unable to find a field named '{0}' (of type {1})"; private const string EXCEPTION_COULD_NOT_ACCESS_FIELD_AT_INDEX = "Unable to find a field named '{0}' at the requested index (of type {1})"; #endregion #region Constructors /// <summary> /// Creates a new AutoType for methods that return Anonymus types /// </summary> public AnonymousType(object type) { this._Init(type, false); } /// <summary> /// Creates a new AutoType for methods that return Anonymus types and /// detetrmins if exceptions should be thrown if a type is missing /// </summary> public AnonymousType(object type, bool supressErrors) { this._Init(type, supressErrors); } /// <summary> /// Initalizes the data for the is type /// </summary> private void _Init(object type, bool supressErrors) { this.SupressExceptions = supressErrors; this.m_Type = type.GetType(); this.m_TypeData = type; } #endregion #region Static Routines /// <summary> /// Creates a new Anonymous Type from the provided object data /// </summary> public static AnonymousType Create(object data) { return new AnonymousType(data); } /// <summary> /// Creates a new Anonymous Type from the provided object data /// </summary> public static AnonymousType Create(object data, bool supressErrors) { return new AnonymousType(data, supressErrors); } #endregion #region Private Members /// <summary> /// The type that will be accessed via reflection /// </summary> private Type m_Type; /// <summary> /// The actual typs that is being used /// </summary> private object m_TypeData; #endregion #region Properties /// <summary> /// Determines if errors should be thrown if any casting errors take place /// </summary> public bool SupressExceptions { get; set; } /// <summary> /// Accessess a property by name and returns an object /// </summary> public object this[string property] { get { return this.Get<object>(property); } } #endregion #region Public Methods /// <summary> /// Checks if this Anonymous Type has the specified property /// </summary> public bool Has(string property) { return ((m_Type.GetProperty(property) as PropertyInfo) != null); } /// <summary> /// Returns if this Anonymous type has the specified property and that /// the value matches the type specified /// </summary> public bool Has(string property, Type isType) { //try and get the property PropertyInfo prop = m_Type.GetProperty(property) as PropertyInfo; //If this type doesn't exist at all, just return false if (prop == null) { return false; } //if it does exist, verify the type if (prop.PropertyType.Equals(isType)) { return true; } return false; } /// <summary> /// Returns a type value using the specified type /// </summary> public T Get<T>(string property) { //return this value if needed PropertyInfo prop = m_Type.GetProperty(property) as PropertyInfo; try { return (T)prop.GetValue(this.m_TypeData, null); } catch (Exception ex) { if (this.SupressExceptions) { return default(T); } throw new Exception( string.Format(EXCEPTION_COULD_NOT_ACCESS_FIELD, property, typeof(T).Name), ex ); } } /// <summary> /// Returns a type value using the specified type /// </summary> public T Get<T>(string property, object[] index) { //return this value if needed PropertyInfo prop = m_Type.GetProperty(property) as PropertyInfo; try { return (T)prop.GetValue(this.m_TypeData, index); } catch (Exception ex) { if (this.SupressExceptions) { return default(T); } throw new Exception( string.Format(EXCEPTION_COULD_NOT_ACCESS_FIELD_AT_INDEX, property, typeof(T).Name), ex ); } } /// <summary> /// Returns a type value using the specified type but includes a default value /// if one it missing /// </summary> public T Get<T>(string property, T defaultValue) { //return this value if needed PropertyInfo prop = m_Type.GetProperty(property) as PropertyInfo; if (prop == null) { return defaultValue; } try { return (T)prop.GetValue(this.m_TypeData, null); } catch (Exception ex) { if (this.SupressExceptions) { return defaultValue; } throw new Exception( string.Format(EXCEPTION_COULD_NOT_ACCESS_FIELD, prop, typeof(T).Name), ex ); } } /// <summary> /// Accepts a delegate that will use the names of the passed in /// parameters as properties to map to. If the property does not /// exist, then the method will fail. /// </summary> public void Use<T1>(Action<T1> with) { //set a default for each of the params T1 param1 = default(T1); //get the parameters for this method var paramList = with.Method.GetParameters(); //update each of the parameters string paramName = string.Empty; try { for (int i = 0; i < paramList.Length; i++) { //find the correct matching property for this parameter paramName = paramList[i].Name; switch (i + 1) { case 1: param1 = this.Get<T1>(paramName); break; } } } catch (Exception ex) { throw new ArgumentException( string.Format(EXCEPTION_MISSING_PARAMETER_INFORMATION, paramName), ex ); } //otherwise, execute the method provided with(param1); } /// <summary> /// Accepts a delegate that will use the names of the passed in /// parameters as properties to map to. If the property does not /// exist, then the method will fail. /// </summary> public void Use<T1, T2>(Action<T1, T2> with) { //set a default for each of the params T1 param1 = default(T1); T2 param2 = default(T2); //get the parameters for this method var paramList = with.Method.GetParameters(); //update each of the parameters string paramName = string.Empty; try { for (int i = 0; i < paramList.Length; i++) { //find the correct matching property for this parameter paramName = paramList[i].Name; switch (i + 1) { case 1: param1 = this.Get<T1>(paramName); break; case 2: param2 = this.Get<T2>(paramName); break; } } } catch (Exception ex) { throw new ArgumentException( string.Format(EXCEPTION_MISSING_PARAMETER_INFORMATION, paramName), ex ); } //otherwise, execute the method provided with(param1, param2); } /// <summary> /// Accepts a delegate that will use the names of the passed in /// parameters as properties to map to. If the property does not /// exist, then the method will fail. /// </summary> public void Use<T1, T2, T3>(Action<T1, T2, T3> with) { //set a default for each of the params T1 param1 = default(T1); T2 param2 = default(T2); T3 param3 = default(T3); //get the parameters for this method var paramList = with.Method.GetParameters(); //update each of the parameters string paramName = string.Empty; try { for (int i = 0; i < paramList.Length; i++) { //find the correct matching property for this parameter paramName = paramList[i].Name; switch (i + 1) { case 1: param1 = this.Get<T1>(paramName); break; case 2: param2 = this.Get<T2>(paramName); break; case 3: param3 = this.Get<T3>(paramName); break; } } } catch (Exception ex) { throw new ArgumentException( string.Format(EXCEPTION_MISSING_PARAMETER_INFORMATION, paramName), ex ); } //otherwise, execute the method provided with(param1, param2, param3); } /// <summary> /// Accepts a delegate that will use the names of the passed in /// parameters as properties to map to. If the property does not /// exist, then the method will fail. /// </summary> public void Use<T1, T2, T3, T4>(Action<T1, T2, T3, T4> with) { //set a default for each of the params T1 param1 = default(T1); T2 param2 = default(T2); T3 param3 = default(T3); T4 param4 = default(T4); //get the parameters for this method var paramList = with.Method.GetParameters(); //update each of the parameters string paramName = string.Empty; try { for (int i = 0; i < paramList.Length; i++) { //find the correct matching property for this parameter paramName = paramList[i].Name; switch (i + 1) { case 1: param1 = this.Get<T1>(paramName); break; case 2: param2 = this.Get<T2>(paramName); break; case 3: param3 = this.Get<T3>(paramName); break; case 4: param4 = this.Get<T4>(paramName); break; } } } catch (Exception ex) { throw new ArgumentException( string.Format(EXCEPTION_MISSING_PARAMETER_INFORMATION, paramName), ex ); } //otherwise, execute the method provided with(param1, param2, param3, param4); } #endregion #region Working With Arrays /// <summary> /// Returns the specified property as an array of AnonymousTypes /// </summary> public AnonymousType[] AsArray(string property) { object[] values = this.Get<object[]>(property); return values.Select(o => { if (o is AnonymousType) { return (AnonymousType)o; } return new AnonymousType(o); }).ToArray(); } /// <summary> /// Performs the specified action on each value in an array of AnonymousTypes /// </summary> public void WithEach(string property, Action<AnonymousType> action) { foreach (AnonymousType value in this.AsArray(property)) { action(value); } } #endregion #region Static Methods /// <summary> /// Returns the type of data for the provided object /// </summary> public static T Get<T>(object data, string property) { return new AnonymousType(data).Get<T>(property); } /// <summary> /// Returns the type of data for the provided object /// </summary> public static T Get<T>(object data, string property, T defaultValue) { return new AnonymousType(data).Get<T>(property, defaultValue); } /// <summary> /// Returns the type of data for the provided object /// </summary> public static AnonymousType[] AsArray(object data, string property) { return new AnonymousType(data).AsArray(property); } /// <summary> /// Performs the following action on each of the values in the specified /// property value for a user /// </summary> public static void WithEach(object data, string property, Action<AnonymousType> action) { new AnonymousType(data).WithEach(property, action); } #endregion } } 

Answer 3

Consider explicitly listing and listing ViewData:

 ViewData["QUsers"] = (from u in db.Users select u).ToList(); foreach(Users u in (List<Users>)ViewData["QUsers"]){ /*Print the data here*/ } 

You can transfer data in several ways, using ViewData, as you above, or TempData to transfer actions. You can also use ViewData.Model to contain a strongly typed model. Note that you will have to change the definition of the view as something like

 ViewPage<User> 

For a good repeater replacement, try http://www.codeplex.com/MVCContrib . They have a Grid Html helper that can help.

Answer 4

If you want to avoid creating a separate class just to display your single projection, you can also resort to using a dictionary, for example:

 from person in personList select new Dictionary<string, string> { { "Name", person.Firstname + " " + person.Lastname }, { "Id", person.Id.ToString() } }; 

Then you can enter your watch page.

 ViewPage<IEnumerable<Dictionary<string, string>>> 

And finally, let's move on to the list in the view like this:

 <% foreach (Dictionary<string, string> p in (IEnumerable)ViewData.Model) { %> <li> <%=p["Id"] %> - <%= p["Name"] %> </li> <% } %> 

Needless to say, the disadvantage is that your code is currently pretty full of “magic lines”, which makes it more error prone due to the lack of compile time checking.

Answer 5

Can't you use RouteValueDictionary from MVC?

Answer 6

I suspect you're looking for a ViewModel: http://msdn.microsoft.com/en-us/vs2010trainingcourse_aspnetmvc3fundamentals_topic7.aspx