I'm trying to pass a value from my database to the view in asp.net mvc, very simple stuff
public ActionResult SettingsList() {
using (podio_doc_db db = new podio_doc_db() ) {
string app_id = db.Configs.Where(r => r.Key == "app.id").Select(r => r.Value).First();
ViewBag["app_id"] = app_id;
}
return View();
}
However I keep getting this error
Cannot apply indexing with [] to an expression of type 'System.Dynamic.DynamicObject'
It should be this instead:
ViewBag.app_id = app_id;
ViewBag is a dynamic type, meaning you can add parameters, like app_id, at run-time.
Related
I am trying to do a simple JSON return but I am having issues I have the following below.
public JsonResult GetEventData()
{
var data = Event.Find(x => x.ID != 0);
return Json(data);
}
I get a HTTP 500 with the exception as shown in the title of this question. I also tried
var data = Event.All().ToList()
That gave the same problem.
Is this a bug or my implementation?
It seems that there are circular references in your object hierarchy which is not supported by the JSON serializer. Do you need all the columns? You could pick up only the properties you need in the view:
return Json(new
{
PropertyINeed1 = data.PropertyINeed1,
PropertyINeed2 = data.PropertyINeed2
});
This will make your JSON object lighter and easier to understand. If you have many properties, AutoMapper could be used to automatically map between DTO objects and View objects.
I had the same problem and solved by using Newtonsoft.Json;
var list = JsonConvert.SerializeObject(model,
Formatting.None,
new JsonSerializerSettings() {
ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore
});
return Content(list, "application/json");
This actually happens because the complex objects are what makes the resulting json object fails.
And it fails because when the object is mapped it maps the children, which maps their parents, making a circular reference to occur. Json would take infinite time to serialize it, so it prevents the problem with the exception.
Entity Framework mapping also produces the same behavior, and the solution is to discard all unwanted properties.
Just expliciting the final answer, the whole code would be:
public JsonResult getJson()
{
DataContext db = new DataContext ();
return this.Json(
new {
Result = (from obj in db.Things select new {Id = obj.Id, Name = obj.Name})
}
, JsonRequestBehavior.AllowGet
);
}
It could also be the following in case you don't want the objects inside a Result property:
public JsonResult getJson()
{
DataContext db = new DataContext ();
return this.Json(
(from obj in db.Things select new {Id = obj.Id, Name = obj.Name})
, JsonRequestBehavior.AllowGet
);
}
To sum things up, there are 4 solutions to this:
Solution 1: turn off ProxyCreation for the DBContext and restore it in the end.
private DBEntities db = new DBEntities();//dbcontext
public ActionResult Index()
{
bool proxyCreation = db.Configuration.ProxyCreationEnabled;
try
{
//set ProxyCreation to false
db.Configuration.ProxyCreationEnabled = false;
var data = db.Products.ToList();
return Json(data, JsonRequestBehavior.AllowGet);
}
catch (Exception ex)
{
Response.StatusCode = (int)HttpStatusCode.BadRequest;
return Json(ex.Message);
}
finally
{
//restore ProxyCreation to its original state
db.Configuration.ProxyCreationEnabled = proxyCreation;
}
}
Solution 2: Using JsonConvert by Setting ReferenceLoopHandling to ignore on the serializer settings.
//using using Newtonsoft.Json;
private DBEntities db = new DBEntities();//dbcontext
public ActionResult Index()
{
try
{
var data = db.Products.ToList();
JsonSerializerSettings jss = new JsonSerializerSettings { ReferenceLoopHandling = ReferenceLoopHandling.Ignore };
var result = JsonConvert.SerializeObject(data, Formatting.Indented, jss);
return Json(result, JsonRequestBehavior.AllowGet);
}
catch (Exception ex)
{
Response.StatusCode = (int)HttpStatusCode.BadRequest;
return Json(ex.Message);
}
}
Following two solutions are the same, but using a model is better because it's strong typed.
Solution 3: return a Model which includes the needed properties only.
private DBEntities db = new DBEntities();//dbcontext
public class ProductModel
{
public int Product_ID { get; set;}
public string Product_Name { get; set;}
public double Product_Price { get; set;}
}
public ActionResult Index()
{
try
{
var data = db.Products.Select(p => new ProductModel
{
Product_ID = p.Product_ID,
Product_Name = p.Product_Name,
Product_Price = p.Product_Price
}).ToList();
return Json(data, JsonRequestBehavior.AllowGet);
}
catch (Exception ex)
{
Response.StatusCode = (int)HttpStatusCode.BadRequest;
return Json(ex.Message);
}
}
Solution 4: return a new dynamic object which includes the needed properties only.
private DBEntities db = new DBEntities();//dbcontext
public ActionResult Index()
{
try
{
var data = db.Products.Select(p => new
{
Product_ID = p.Product_ID,
Product_Name = p.Product_Name,
Product_Price = p.Product_Price
}).ToList();
return Json(data, JsonRequestBehavior.AllowGet);
}
catch (Exception ex)
{
Response.StatusCode = (int)HttpStatusCode.BadRequest;
return Json(ex.Message);
}
}
JSON, like xml and various other formats, is a tree-based serialization format. It won't love you if you have circular references in your objects, as the "tree" would be:
root B => child A => parent B => child A => parent B => ...
There are often ways of disabling navigation along a certain path; for example, with XmlSerializer you might mark the parent property as XmlIgnore. I don't know if this is possible with the json serializer in question, nor whether DatabaseColumn has suitable markers (very unlikely, as it would need to reference every serialization API)
add [JsonIgnore] to virtuals properties in your model.
Using Newtonsoft.Json: In your Global.asax Application_Start method add this line:
GlobalConfiguration.Configuration.Formatters.JsonFormatter.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore;
Its because of the new DbContext T4 template that is used for generating the EntityFramework entities. In order to be able to perform the change tracking, this templates uses the Proxy pattern, by wrapping your nice POCOs with them. This then causes the issues when serializing with the JavaScriptSerializer.
So then the 2 solutions are:
Either you just serialize and return the properties you need on the client
You may switch off the automatic generation of proxies by setting it on the context's configuration
context.Configuration.ProxyCreationEnabled = false;
Very well explained in the below article.
http://juristr.com/blog/2011/08/javascriptserializer-circular-reference/
Provided answers are good, but I think they can be improved by adding an "architectural" perspective.
Investigation
MVC's Controller.Json function is doing the job, but it is very poor at providing a relevant error in this case. By using Newtonsoft.Json.JsonConvert.SerializeObject, the error specifies exactly what is the property that is triggering the circular reference. This is particularly useful when serializing more complex object hierarchies.
Proper architecture
One should never try to serialize data models (e.g. EF models), as ORM's navigation properties is the road to perdition when it comes to serialization. Data flow should be the following:
Database -> data models -> service models -> JSON string
Service models can be obtained from data models using auto mappers (e.g. Automapper). While this does not guarantee lack of circular references, proper design should do it: service models should contain exactly what the service consumer requires (i.e. the properties).
In those rare cases, when the client requests a hierarchy involving the same object type on different levels, the service can create a linear structure with parent->child relationship (using just identifiers, not references).
Modern applications tend to avoid loading complex data structures at once and service models should be slim. E.g.:
access an event - only header data (identifier, name, date etc.) is loaded -> service model (JSON) containing only header data
managed attendees list - access a popup and lazy load the list -> service model (JSON) containing only the list of attendees
Avoid converting the table object directly. If relations are set between other tables, it might throw this error.
Rather, you can create a model class, assign values to the class object and then serialize it.
I'm Using the fix, Because Using Knockout in MVC5 views.
On action
return Json(ModelHelper.GetJsonModel<Core_User>(viewModel));
function
public static TEntity GetJsonModel<TEntity>(TEntity Entity) where TEntity : class
{
TEntity Entity_ = Activator.CreateInstance(typeof(TEntity)) as TEntity;
foreach (var item in Entity.GetType().GetProperties())
{
if (item.PropertyType.ToString().IndexOf("Generic.ICollection") == -1 && item.PropertyType.ToString().IndexOf("SaymenCore.DAL.") == -1)
item.SetValue(Entity_, Entity.GetPropValue(item.Name));
}
return Entity_;
}
You can notice the properties that cause the circular reference. Then you can do something like:
private Object DeCircular(Object object)
{
// Set properties that cause the circular reference to null
return object
}
//first: Create a class as your view model
public class EventViewModel
{
public int Id{get;set}
public string Property1{get;set;}
public string Property2{get;set;}
}
//then from your method
[HttpGet]
public async Task<ActionResult> GetEvent()
{
var events = await db.Event.Find(x => x.ID != 0);
List<EventViewModel> model = events.Select(event => new EventViewModel(){
Id = event.Id,
Property1 = event.Property1,
Property1 = event.Property2
}).ToList();
return Json(new{ data = model }, JsonRequestBehavior.AllowGet);
}
An easier alternative to solve this problem is to return an string, and format that string to json with JavaScriptSerializer.
public string GetEntityInJson()
{
JavaScriptSerializer j = new JavaScriptSerializer();
var entityList = dataContext.Entitites.Select(x => new { ID = x.ID, AnotherAttribute = x.AnotherAttribute });
return j.Serialize(entityList );
}
It is important the "Select" part, which choose the properties you want in your view. Some object have a reference for the parent. If you do not choose the attributes, the circular reference may appear, if you just take the tables as a whole.
Do not do this:
public string GetEntityInJson()
{
JavaScriptSerializer j = new JavaScriptSerializer();
var entityList = dataContext.Entitites.toList();
return j.Serialize(entityList );
}
Do this instead if you don't want the whole table:
public string GetEntityInJson()
{
JavaScriptSerializer j = new JavaScriptSerializer();
var entityList = dataContext.Entitites.Select(x => new { ID = x.ID, AnotherAttribute = x.AnotherAttribute });
return j.Serialize(entityList );
}
This helps render a view with less data, just with the attributes you need, and makes your web run faster.
#Html.Partial("~/Areas/WO/Views/PartialContent/_FirstPage.cshtml", new ViewDataDictionary { { "WOID", WOID } })
In my Page i am accessing Partial view in the above way.
I need to pass WOID(view data dictionary) value from query string, For that i am using following Code
#{
var desc = Html.ViewContext.HttpContext.Request.QueryString.Get("ID");
Uri referrer = HttpContext.Current.Request.UrlReferrer;
string[] query = referrer.Query.Split('=');
int WOID = Convert.ToInt32(query[1]);
}
But the issue is this code is working in all browsers except I.E. i Need to Solve this problem.
Please help me
Instead of this you can have this value as part of you model and use that.That is the standard and recommeded way .
In your action method you can have these as parameter.Your query string value will get bind to this parameter
public ActionResult ActionMethod(int ID)
{
Model.WOID = WOID;
// Other logic
return View(Model)
}
Next step you can add this as a property to your view model or add it to ViewData dictionary and then access it in your partial view.
In the RedirectToAction below, I'd like to pass a viewmodel. How do I pass the model to the redirect?
I set a breakpoint to check the values of model to verify the model is created correctly. It is correct but the resulting view does not contain the values found in the model properties.
//
// model created up here...
//
return RedirectToAction("actionName", "controllerName", model);
ASP.NET MVC 4 RC
RedirectToAction returns a 302 response to the client browser and thus the browser will make a new GET request to the url in the location header value of the response came to the browser.
If you are trying to pass a simple lean-flat view model to the second action method, you can use this overload of the RedirectToAction method.
protected internal RedirectToRouteResult RedirectToAction(
string actionName,
string controllerName,
object routeValues
)
The RedirectToAction will convert the object passed(routeValues) to a query string and append that to the url(generated from the first 2 parameters we passed) and will embed the resulting url in the location header of the response.
Let's assume your view model is like this
public class StoreVm
{
public int StoreId { get; set; }
public string Name { get; set; }
public string Code { set; get; }
}
And you in your first action method, you can pass an object of this to the RedirectToAction method like this
var m = new Store { StoreId =101, Name = "Kroger", Code = "KRO"};
return RedirectToAction("Details","Store", m);
This code will send a 302 response to the browser with location header value as
Store/Details?StoreId=101&Name=Kroger&Code=KRO
Assuming your Details action method's parameter is of type StoreVm, the querystring param values will be properly mapped to the properties of the parameter.
public ActionResult Details(StoreVm model)
{
// model.Name & model.Id will have values mapped from the request querystring
// to do : Return something.
}
The above will work for passing small flat-lean view model. But if you want to pass a complex object, you should try to follow the PRG pattern.
PRG Pattern
PRG stands for POST - REDIRECT - GET. With this approach, you will issue a redirect response with a unique id in the querystring, using which the second GET action method can query the resource again and return something to the view.
int newStoreId=101;
return RedirectToAction("Details", "Store", new { storeId=newStoreId} );
This will create the url Store/Details?storeId=101
and in your Details GET action, using the storeId passed in, you will get/build the StoreVm object from somewhere (from a service or querying the database etc)
public ActionResult Details(string storeId)
{
// from the storeId value, get the entity/object/resource
var store = yourRepo.GetStore(storeId);
if(store!=null)
{
// Map the the view model
var storeVm = new StoreVm { Id=storeId, Name=store.Name,Code=store.Code};
return View(storeVm);
}
return View("StoreNotFound"); // view to render when we get invalid store id
}
TempData
Following the PRG pattern is a better solution to handle this use case. But if you don't want to do that and really want to pass some complex data across Stateless HTTP requests, you may use some temporary storage mechanism like TempData
TempData["NewCustomer"] = model;
return RedirectToAction("Index", "Users");
And read it in your GET Action method again.
public ActionResult Index()
{
var model=TempData["NewCustomer"] as Customer
return View(model);
}
TempData uses Session object behind the scene to store the data. But once the data is read the data is terminated.
Rachel has written a nice blog post explaining when to use TempData /ViewData. Worth to read.
Using TempData to pass model data to a redirect request in Asp.Net Core
In Asp.Net core, you cannot pass complex types in TempData. You can pass simple types like string, int, Guid etc.
If you absolutely want to pass a complex type object via TempData, you have 2 options.
1) Serialize your object to a string and pass that.
Here is a sample using Json.NET to serialize the object to a string
var s = Newtonsoft.Json.JsonConvert.SerializeObject(createUserVm);
TempData["newuser"] = s;
return RedirectToAction("Index", "Users");
Now in your Index action method, read this value from the TempData and deserialize it to your CreateUserViewModel class object.
public IActionResult Index()
{
if (TempData["newuser"] is string s)
{
var newUser = JsonConvert.DeserializeObject<CreateUserViewModel>(s);
// use newUser object now as needed
}
// to do : return something
}
2) Set a dictionary of simple types to TempData
var d = new Dictionary<string, string>
{
["FullName"] = rvm.FullName,
["Email"] = rvm.Email;
};
TempData["MyModelDict"] = d;
return RedirectToAction("Index", "Users");
and read it later
public IActionResult Index()
{
if (TempData["MyModelDict"] is Dictionary<string,string> dict)
{
var name = dict["Name"];
var email = dict["Email"];
}
// to do : return something
}
Another way to do it is to store it in the session.
var s = JsonConvert.SerializeObject(myView);
HttpContext.Session.SetString("myView", s);
and to get it back
string s = HttpContext.Session.GetString("myView");
myView = JsonConvert.DeserializeObject<MyView>(s);
I feel a bit absurd asking this but I can't find a way to get parameters for a get request at
/api/foo?sort=name for instance.
In the ApiController class, I gave a public string Get(). Putting Get(string sort) makes /api/foo a bad request. Request instance in the ApiController is of type System.Net.Http.HttpRequestMessage. It doesn't have a QueryString or Parameters property or anything.
The ApiController is designed to work without the HttpContext object (making it portable, and allowing it to be hosted outside of IIS).
You can still access the query string parameters, but it is done through the following property:
Request.GetQueryNameValuePairs()
Here's an example loop through all the values:
foreach (var parameter in Request.GetQueryNameValuePairs())
{
var key = parameter.Key;
var value = parameter.Value;
}
You could just use
HttpContext.Current.Request.QueryString
Here's an example that gets the querystring q from the request and uses it to query accounts:
var q = Request.GetQueryNameValuePairs().Where(nv => nv.Key =="q").Select(nv => nv.Value).FirstOrDefault();
if (q != null && q != string.Empty)
{
var result = accounts.Where(a=>a.Name.ToLower().StartsWith(q.ToLower()));
return result;
}
else
{
throw new Exception("Please specify a search query");
}
This can be called then like this:
url/api/Accounts?q=p
Get all querystring name/value pairs into a variable:
IEnumerable<KeyValuePair<string, string>> queryString = request.GetQueryNameValuePairs();
Then extract a specified querystring parameter
string value = queryString.Where(nv => nv.Key == "parameterNameGoesHere").Select(nv => nv.Value).FirstOrDefault();
You can also use the following
var value = request.GetQueryNameValuePairs().Where(m => m.Key == "paramName").SingleOrDefault().Value;
if we have a proper model for that request
for example
public class JustModel
{
public int Id {get;set;}
public int Age {gets;set;}
}
and query like this
/api/foo?id=1&Age=10
You could just use [FromUri] attribute
For example
public IHttpActionResult GetAge([FromUri] JustModel model){}
You're trying to build an OData webservice? If so, just return an IQueryable, and the Web API will do the rest.
Adding a default value does the job:
public string Get(string sort="")
The recommended approach for passing lists of values as a QueryString is
www.site.com/search?value=1&value=2&value=3&value=4
ASP.NET handles this well:
string value = QueryString.Get("value"); // returns "1,2,3,4"
But I can't figure out a way of passing these values by into RouteData. The obvious approach would be to add
int[] value = {1,2,3,4};
into the RouteData and have super smart MVC sort things out for me. Unfortunately MVC is dump when it comes to passing arrays into RouteData, it basically calls .ToString() adding value=int[] to my QueryString.
I tried adding the values to RouteValueDictionary (but being a dictionary can't handle this:)
RouteValueDictionary dict = new RouteValueDictionary();
dict.Add("value","1");
dict.Add("value","2"); // Throws Exception (Keys must be unique)
I could try passing values like this:
www.site.com/search?value=1,2,3,4
but this is Encoded to the URL as
www.site.com/search?value=1%2C2%2C3%2C4
I'm not sure if this is a bad thing or not,but it sure looks bad.
So, how do you pass lists of values as RouteData in ASP.NET MVC. Is there any way I can add to MVC to make it handle an int[]? Or is the underlying Dictionary-based data structure a show-stopper for passing lists of values easily to ASP.NET MVC?
I've come up with a solution to this myself by making a new class RouteDataList()
public class RouteDataList<T> : List<T>
{
public RouteDataList(IEnumerable<T> enumerable) : base(enumerable) { }
public RouteDataList() : base() { }
public override string ToString()
{
string output = "";
for (int i = 0; i < this.Count; i++)
{
output += i < this.Count - 1 ? this[i] + "-" : this[i].ToString();
}
return output;
}
public static List<Int32> ParseInts(string input)
{
if (String.IsNullOrEmpty(input)) return null;
List<Int32> parsedList = new List<int>();
string[] split = input.Split('-');
foreach (string s in split)
{
int value;
if(Int32.TryParse(s, out value)) parsedList.Add(value);
}
return parsedList;
}
}
Use as follows:
RouteDataList<Int32> valuelist = new RouteDataList<Int32>(){5,6,7,8};
RouteDataList<Int32> anothervaluelist = new RouteDataList<Int32>(){12,13,14,15};
Then Pass to any function that takes a RouteValueDictionary/Anonymous Type:
return RedirectToAction("View", "Browse", new {valuelist, anothervaluelist } );
// Produces http://www.site.com/browse/view?valuelist=5-6-7-8&anothervaluelist=12-13-14-15
// To Parse back to a list:
List<Int32> values = RouteDataList<Int32>.ParseInts(HttpContext.Current.Request.QueryString["valuelist"])