I am creating a project using ASP.NET MVC 5.
I used Identity to get user information.
Using migrations I created fields like FirstName, LastName
But how do I use that? I have this:
#using MTC.Models
#helper Render(MTC.Post post, System.Web.Mvc.HtmlHelper html, bool showComments)
{
{
var user = new ApplicationUser();
user.FirstName.ToString();
}
}
And it returns this:
System.NullReferenceException: Object reference not set to an instance of an object.
All I want to do is get it to display the name from the database.
I am trying to learn the backend. Sorry If this is completely wrong.
you are creating new object of ApplicationUser without initializing its values. So every property of this object will be null. You need to either first assign value to it or fetch user from database.
You can do this by creating UserID column in your table along with Names of user and get User Name from the table by:
string Name = User.Identity.GetUserId();
return View(Database.Table.Where(r =>r.UserID == Name).ToList());
You can do this in your controller and also in your view.
Related
Grails will create an id and a version columns from a domain class automatically. I want to use my own column for the primary key. So, I follow the doc to change the mapping.
class book {
String isbn
static mapping = {
id generator: 'assigned', name: 'isbn'
}
}
So far so good. The isbn column is now the primary key.
I use generate-all to create the view and controller. However, the data binding won't work anymore.
Create and Save work no problem. It binds a book to the view. I can add a new book to the database no problem.
def create() {
respond new Book(params)
}
def save(Book book) {
if (book == null) {
notFound()
return
}
...
}
But the Update action does not bind. book is null after I click the Update button from the Edit view.
def update(Book book) {
if (book == null) {
notFound()
return
}
...
}
The codes generated by generate-all in the Save and Update actions are the same. I don't understand why it will bind the book to the Save action but not to Update action.
Would you show me the problem please?
Many Thanks!
I think I figure it out. When I bind an object to a view, Grails is hardcoded to look for the id property. It has to be spelled "id". If there is no "id" property in the domain class, Grails will not bind.
The way I figure this out is to look at the actual HTML generated by the server.
If there is an id property bind to the view, I see the HTML has the ../controller/action/id link.
If the id property is missing, the HTML link is just ../controller/index
I am new to Grails. So, I guess in order for the binding to work, I need to have an id property for Grails to put in the link.
I think this is a REST call. I don't know what REST is though.
So, I will try to add an dummy id property to my Book domain class to see if Grails will take the bait. I will set up the domain so Grails won't generate the id column in the database table. The id property is used locally only. No need to save it to the database.
class book {
String isbn
String id
static mapping = {
id generator: 'assigned', name: 'isbn'
}
}
I will copy the isbn value to the id property. I am not sure if this will work or not. I hope Grails will generate the link in the view with the isbn string in the id property instead of the default integer id value.
../controller/action/978-3-16-148410-0
So I basically have the same issue as this post: ASP.NET MVC - How to populate dropdownlist with another model?
The solution works... technically.. as long as the model is populated. However, I'm working with a CREATE view where the controller's action simply returns a blank "View()" obviously because it's creating something so you don't have any data yet.... yet I obviously still want the dropdownlist to populate from a model which gets it's data from the DB. If I try to run this code on a view with an empty model I get "Object reference not set to object" when it tries to grab the property that returns the list.
I tried instantiating a new, blank model in the Create action with the USING statement and set only PropertyTypeList property with a new instance of the Type model, and passed it to the view and it sort of worked... the view showed up with the dropdown of the other Type model populated, but it pre-filled in a bunch of the int/date types with 0's and 1/1/1900's because I have non-nullable fields. This is the closest I've gotten so far to simply letting the user create a new record with a pre-populated dropdown from ome of the fields that comes from a model.
I could just create a new Type model in the Create Action and assign it to the Viewbag or Tempdata, which I've done in the past, but this idea just makes me feel DIRTY. Viewbag disappears if the person refreshes the page so they get an error and is totally unprofessional. And I don't use Tempdata much because it relies on session state which gets very problematic if a user has my form open in mulitple tabs which could easily happen.
I feel like the solution from this post is SO close. It works fine when you're working with the EDIT action because you're passing a full model. But does anyone know how to get a dropdownlist to populate like this with an empty model? I tried something like adding an extra class to my secondary Type model
namespace blablanamespace {
public partial class PropertyType {
.. bla bla bla propertytype ID and name here
}
public class ViewModel
{
private readonly List<PropertyType> _keytypes;
public IEnumerable<SelectListItem> PropTypeItems
{
get { return new SelectList(_keytypes, "TypeID", "TypeID"); }
}
}
}
and
#Html.DropDownListFor(model => model.TypeID, new SelectList(new blablanamespace.Models.ViewModel().PropTypeItems))
but then I just get this error:
Value cannot be null. Parameter name: items
If I change the ViewModel class to instantiate a new list of types like so
public class ViewModel
{
public class ViewModel
{
private readonly List<PropertyType> _keytypes = new List<PropertyType>;
public IEnumerable<SelectListItem> PropTypeItems
{
get { return new SelectList(_keytypes, "TypeID", "TypeID"); }
}
}
I don't get the error this time, but I just get a blank form(yay) with a blank dropdownlist(boo!!). I figured this latter method would work since when I want to populate a new fresh list in the controller I basically do the same thing
List<ApplicationKeyType> _keytypes = new List<ApplicationKeyType>();
That behavior doesn't appear to be the same in the model.
I have a project with a form that is completed over several parts. E.g. Part 1 might include your name, and part 2 your address.
In MVC I have several views which represent each of the parts and one model to hold all the form data.
I would like to save the form data at the completion of each part, and retrieve the saved record on the next part (so that the whole model is available at each stage).
I am using Post-Redirect-Get to avoid the 'form may be resubmitted' warnings from browsers using the back and forward buttons.
Controller code
[HttpGet]
[Route("Form/Part/{id}")]
public ActionResult Part(int id, int? recordId)
{
var model = new MyVM();
if(recordId.HasValue) {
// get record from DB
// map record to 'model'
}
return View("Form.{id}", model);
}
[HttpPost]
[Route("Form/Part/{id}")]
public ActionResult Part(int id, MyVM model)
{
// map model to entity
// save/update entity
return RedirectToAction($"Form/Part/{id + 1}", new { recordId = recordId })
}
My question is how best to retain the ID of the newly created / updated record and pass it to the next form part.
Whilst passing the recordId as a routeValue works, it breaks when I use the browser back button as the recordId in the querystring is lost.
I have considering storing this in the session perhaps, but don't really want to bring the HttpContext into play if I don't have to for testing reasons.
Is there a recommended way to achieve this kind of thing? Any thoughts on the various ways to keep track of the current record would be greatly appreciated.
You can either use the TempData or Session to pass Data between requests.
I Would create a big class / object with all the fields from the wizard, throw it in the session eg key "MyWizardData" and retrieve it in the other parts of the wizard.
After
// save/update entity
you have the ID, throw it in the session and grab it back in the next action.
If you dont want to use the session, get the id after save / update and store it in a field in the database in the user table. Or just store the UserId with your created entity row. Then you can grab it in any action.
There's probably a really basic answer to this question but I am new to Entity and MVC and am getting used to the basics.
I'm trying to automatically generate a MVC controller for the main table Sites with a dropdown for server. It seems like I would need a model like this:
public class Sites
{
public TTSites TTSites { get; set; }
public List<servers> server { get; set; }
public Sites()
{
server = new List<servers>();
}
}
This is using the classes TTSites and servers both with string server
But if I set this as my model class and my entity database as data context it says I need to define a key. Should I be using the base classes instead of the model or what? Do i need to set something up in the model or base class?
It seems like you've got some terminology confused. You code the controller actions in a controller class, and the routing engine determines what controller action to call based on the URL. For example, if you have a HomeController class with a default Index action, it might look like this:
public ActionResult Index()
{
// code here
}
This would be invoked with the default routing, if you went to your site with a URL like this (let's say your site can be hit via the www.mysite.com URL:
http://www.mysite.com/Home
That would get you into the Index action in the controller.
Ordinarily, one would use a view model to use on the UI side, and that would be populated from an entiy with the data you need in the view itself. If you had two entities like TTSite and Server, you'd populate the Sites view model like so, as a (very simple) example:
public ActionResult Index()
{
var servers = yourDbContext.Servers.ToList();
var ttSite = yourDbContext.TTSites.GetByID(1); // retrieve one entity by its ID value, this would be acquired dynamically based on some sort of user input rather than hard-coded
var viewModel = new Sites(servers);
viewModel.TTSite = ttSite;
return View(viewModel);
}
I'm not including anything regarding making drop-downs, just illustrating getting data into a view model and then creating a view with that view model.
Note that you would not use the Sites class as an entity but rather a view model, and setting its data based on entities from your database. You wouldn't be setting any primary keys in a view model class; those are the concern of the data model, and you've presumably already got those entities (such as TTSite) set up in a usable fashion in your data layer.
Once you've got a controller action and a view up and working, you can turn to getting the view model data into a form usable by a drop-down list, and going from there.
I'm using a customized method for tracking individual modified properties of an n-tier disconnected entity class. I extracted it from
Programming Entity Framework: DbContext by Julia Lerman and Rowan
Miller (O’Reilly). Copyright 2012 Julia Lerman and Rowan Miller,
978-1-449-31296-1.
The code is:
public void ApplyChanges<TEntity>(TEntity root) where TEntity : class, IObjectWithState {
// bind the entity back into the context
dbContext.Set<TEntity>().Add(root);
// throw exception if entity does not implement IObjectWithState
CheckForEntitiesWithoutStateInterface(dbContext);
foreach (var entry in dbContext.ChangeTracker.Entries<IObjectWithState>()) {
IObjectWithState stateInfo = entry.Entity;
if (stateInfo.State == RecordState.Modified) {
// revert the Modified state of the entity
entry.State = EntityState.Unchanged;
foreach (var property in stateInfo.ModifiedProperties) {
// mark only the desired fields as modified
entry.Property(property).IsModified = true;
}
} else {
entry.State = ConvertState(stateInfo.State);
}
}
dbContext.SaveChanges();
}
The purpose of this method is to let the EF know only a predefined set of entity fields are ready for update in the next call of SaveChanges(). This is needed in order to workaround the entity works in ASP.NET MVC 3 as follows:
on initial page load: the Get action of the controller is loading the
entity object and passing it as a parameter to the view.
The View generate controls for editing 2 of the fields of the entity,
and holds the ID of the record in a hidden field.
When hitting [save] and posting the entity back to the controller all
of the fields excepting the 3 preserved in the view comes with a null
value. This is the default behavior of the MVC binding manager.
If i save the changes back to the database the update query will of course overwrite the non mapped fields with a sentence as follows:
UPDATE non_mapped_field_1 = NULL, ..., mapped_field_1 = 'mapped_value_1', mapped_field_2 = 'mapped_value_2', ... non_mapped_field_n = NULL WHERE ID = mapped_field_3
This is the reason i'm trying to track the fields individually and update only those fields i'm interested in. before calling the custom method with ApplyChanges() i'm adding the list of fields i want to be included in the update to the IObjectWithState.ModifiedProperties list, in order to get a SQL statement as follows:
UPDATE mapped_field_1 = 'mapped_value_1', mapped_field_2 = 'mapped_value_2' WHERE id = mapped_value_3
The problem is, when marking one of the fields as modified in ApplyChanges, i.e.:
entry.Property(property).IsModified = true;
the system is throwing the following exception:
{System.InvalidOperationException: Member 'IsModified' cannot be called for property 'NotifyCEDeadline' on entity of type 'User' because the property is not part of the Entity Data Model.
at System.Data.Entity.Internal.InternalPropertyEntry.ValidateNotDetachedAndInModel(String method)
at System.Data.Entity.Internal.InternalPropertyEntry.set_IsModified(Boolean value)
at System.Data.Entity.Infrastructure.DbPropertyEntry.set_IsModified(Boolean value)
...
So the question is. There's a way to bypass this EF validation or let the context know of the existance of this system property (IsModified) that i'm trying to change?
Summary of the architeture:
EF Code first (annotation + Fluent API)
Oracle .NET EF Data provider (ODAC)
Context is injected to a cutom business context with nInject.MVC => this is the reason i customized the ApplyChanges() method from
using (var context = new BreakAwayContext()){
context.Set().Add(root);
to a simple call to the already initialized dbcontext
dbContext.Set().Add(root);
Oracle Database is created manually i.e. without the help of EF, so no EF metadata tables are used.
Thanks,
Ivan.
Very good description, however I can't find any information on why you need a transient property called "IsModified" in the object and/or why you need to tell EF about it being modified (EF won't be able to persist it anyway).
The value of the IsModified property should be set by the model binder if the property was incldued in the view anyway.
You could just add code in your ApplyChanges method to skip a property named "IsModified", or even better, filter only known properties using entry.CurrentValues.PropertyNames, e.g.:
foreach (var property in stateInfo.ModifiedProperties) {
// mark only the desired fields as modified
if (entry.CurrentValues.PropertyNames.Contains(property)) {
entry.Property(property).IsModified = true;
}
}
Update: Ivan, very sorry I did not understand the problem better when you posted it several months ago and that I did not follow up after your added these clarifying comments. I think I understand better now. That said, I think the code snippet that I offered can be part of the solution. From looking at the exception you are getting again, I understand now that the problem that EF is detecting is that NotifyCEDDealine is not a persistent property (i.e. it is not mapped in the Code First model to a column in the database). IsModified can only be used against mapped properties, therefore you have two options: you change the code of the implementation of IObjectWithState in your entities so that non-mapped properties are not recorded in ModifiedProperties, or you use my code snippet to prevent calling IsModified with those.
By the way, an alternative to doing all this is to use the Controller.TryUpdateModel API to set only the modified properties in your entities.
Hope this helps (although I understand it is very late).