I have two Dictionary<string, byte> properties in my model that should validate properly with from 0 to 5 items. For example the property skill (string dropDownListLabel, byte years).
Because I need to support non-javascript clients, I render all 5 input pairs to the browser, only binding existing dictionary items, and life is great. This gives 5 empty input pairs for a new plain HTML form, each with unique input names, which I also want.
Here's the serialization (input names) I use:
skill[0].Key = "", skill[0].Value = ""
... three more pairs ...
skill[4].Key = "", skill[4].Value = ""
But on POST, for Key/Value pairs with neither Key nor Value specified, DefaultModelBinder validation errors result on Value.
Is there a type and serialization I can use that will validate in DefaultModelBinder when both or neither Key and Value are POSTed, so MVC does as much work for me as possible, only adding pairs into a collection when they have content?
Thanks,
Shannon
You cannot bind an empty string to a value type (byte) so the default model binder marks your model as invalid. If you want to allow empty values you should use a nullable byte:
Dictionary<string, byte?>
UPDATE:
Another possibility is to use a collection of a custom type containing two properties each representing respectively the key and the value. Then use strongly typed helpers and editor templates in your view so that you don't have to worry about the wire format and finally you will need to ensure that the keys are unique so you will need a custom validator. Personally I use FluentValidation.NET for this part but if you are using data annotations you will need a custom attribute which will be used to decorate the collection property in the view model.
Related
A simple scenario that I've never seen before, but a colleague has just hit - MVC3
Create an action method MyAction(int myProperty = 0)
Create a model that has a property MyProperty
Pass an instance of this model to a strongly typed view, but set the property to 10 in code (don't use the query string parameter!)
In the view, Html.TextBoxFor(x => x.MyProperty)
This should render 10 in the text box.
Now call the action method MyAction?myProperty=8
Shouldn't this still render 10 in the text box?
I see that I can override the property discovered by the expression and assume this is because they are the same name (Query String parameter and model property). Eveything is then in the ViewData but one overrides the other.
Is this by design?
This is by design - ModelState is the highest priority value-provider for model properties, higher than even model itself. Without query string parameter, ModelState does not contain value for MyProperty, so framework uses model value.
You can use ModelState.Remove("MyProperty") to ensure using model value
If you look at the source code for Html.TextBoxFor you will see that if a value exists in ModelState then it will always use that value before any other.
string attemptedValue = (string)htmlHelper.GetModelStateValue(fullName, typeof(string));
tagBuilder.MergeAttribute("value", attemptedValue ?? ((useViewData) ? htmlHelper.EvalString(fullName, format) : valueParameter), isExplicitValue);
If the value is in ModelState, then it doesn't matter what you set in code.
I have a site where I'm using fluentNhibernate and Asp.net MVC. I have an Edit view that allows user to edit 8 of the 10 properties for that record (object). When you submit the form and the Model binds, the two un-editable fields come back in the view-model as Empty strings or as default DateTime values depending on the type of property.
Because I'm also using AutoMapper to map my view-model to my Domain Entity, I cannot just load a fresh copy of my object from the database and manually set the 2 missing properties. Whats the best way to persist those fields that I don't want edited?
One way that does work is to persist the values in hidden Input fields on my View. That works but feels gross. I appreciate any recommendations. Is there a way in my AutoMapper to configure this desired functionality?
UPDATE:
Ok, So I guess I'm not trying to ignore the fields, I'm trying to make sure that I don't persist null or empty string values. Ignoring the fields in AutoMapper does just that, they get ignored and are null when I attempt to map them before Saved to my repository.
The asp.net mvc DefaultModelBinder is extensible, and you can override it to create your own binding schema. But this will involve more work than two "hidden Input fields", which , in my point of view, is not that gross.
You can tell Automapper to ignore the 2 properties:
Mapper.CreateMap<Source, Destination>()
.ForMember(dest => dest.SomeValuefff, opt => opt.Ignore());
Possible related question.
Can you use the AutoMapper.Map overload that also accepts TEntity?!
entity = Mapper.Map(viewmodel, entity);
As long as you do not have the properties on your viewmodel, it won't change the values on your entity. It takes the entity being passed in and applies only the properties from the viewmodel back to the entity.
I have a fairly complex ViewModel containing decimal properties, which are exposed to the user in the form of text boxes. I want a textbox with no value to be interpreted as zero. (The properties in the underlying domain object are non-nullable, and the default value is 0.)
When the DefaultModelBinder binds the view data to the ViewModel, decimal properties with blank strings for inputs are initialized to zero (as is standard in .NET), but the DefaultModelBinder is adding errors to the ModelState for the blank text boxes. As a result the ModelState is invalid and the user sees a whole bunch of "A value is required." errors for the textboxes they left blank.
How can I stop these errors from being added to the ModelState?
The best thing that you could do in this situation is to create a ViewModel. Instead of binding directly to your Domain Model, instead bind to the ViewModel that was created solely for the purpose of Data Transfer to your view. On the ViewModel, you can create these fields as nullable decimals. You can then map the ViewModel back to your Domain Model however you like.
This is really the correct behavior. If you enter nothing in the TextBox then that is equivalent to null, not 0.
I'm building a data entry interface and have successfully bound the columns that have reference tables for their data using DropDownList so the user selects from the pre-configured values.
My problem now is that I don't want the first value to be selected by default, I need to force the user to select a value from the list to avoid errors where they didn't pick that field and by default a value was assigned.
Is there a more elegant way of doing this than to add code to include an empty value at the top of the list after I get it from the database and before i pass it to the SelectList constructor in my controller class?
The Html helper function takes a 'first empty value' parameter as the third argument.
<%=Html.DropDownList("name",dataSource,"-please select item-")%>
You can also use this way:
dropdownlist.DataTextField = ds.Tables[0].Columns[0].Caption;
dropdownlist.DataValueField = ds.Tables[0].Columns[1].Caption;
dropdownlist.DataSource = ds;
dropdownlist.DataBind();
dropdownlist.Items.Insert(0, new ListItem("Select ...", string.Empty));
Short: how does modelbinding pass objects from view to controller?
Long:
First, based on the parameters given by the user through a search form, some objects are retrieved from the database.
These objects are given meta data that are visible(but not defining) to the customer (e.g: naming and pricing of the objects differ from region to region).
Later on in the site, the user can click links that should show details of these objects.
Because these meta data are important for displaying, but not defining, I need to get the previously altered object back in the controller.
When I use the default asp.net mvc modelbinding, the .ToString() method is used. This off course doesn't return a relevant string for recreating the complete object.
I would have figured the ISerializable interface would be involved, but this is not so.
How should I go about to get the desired effect? I can't imagine I'm the first one to be faced with this question, so I guess I'm missing something somewhere...
The default model binding takes form parameters by name and matches them up with the properties of the type specified in the argument list. For example, your model has properties "Price" and "Name", then the form would need to contain inputs with ids/names "Price" and "Name" (I suspect it does a case insensitive match). The binder uses reflection to convert the form values associated with these keys into the appropriate type and assigns it to the properties of a newly created object of the type specified by the parameter (again derived by reflection).
You can actually look at (and download) the source for this at http://www.codeplex.com/aspnet, although you'll have to drill down into the MVC source from there. I'd give a link to the DefaultModelBinder source, but the way they are constructed, I believe the link changes as revisions are introduced.
So, to answer your question, you need to have parameters (could be hidden) on your form that correspond to the properties of the object that you want to recreate. When you POST the form (in the view) to the controller, the binder should reconstitute an object of the specified type using the form parameters. If you need to do translation from the values in the form parameter to the object properties, you'll probably need to implement your own custom model binder.
[EDIT] In response to your second post:
Let's say that we want to have a link back to an action that uses a customized object. We can store the customized object in TempData (or the Session if we need it to last more through more than one postback) with a particular key. We can then construct the action link and provide the key of the object as value to the ActionLink in an anonymous class. This will pass back the key as a Request parameter. In our action we can use the key from this parameter to retrieve the object from TempData.
<%= Html.ActionLink( ViewData["CustomObject1",
"Select",
new { TempDataKey = ViewData["CustomObject1_Key"] }
) %>
public ActionResult Select()
{
Entity custObj = null;
string objKey = Request.Params["TempDataKey"];
if (!string.IsNullOrEmpty(objKey))
{
custObj = (Entity)TempData[objKey];
}
... continue processing
}
#tvanfosson
Thanks for your explanation, but what about links? (no forms involved)
Currently the Html.ActionLink(c=>c.Action(parameter), "label") takes objects as parameter. These have to be translated into URL parts. For this, MVC ALWAYS goes to the .ToString() method. I don't want to serialize my object in the ToString method.
Shouldn't I be able to somehow help the framework serialize my object? Say through the ISerialize interface or something?