I have succesfully extended the EF6 designer to allow for some custom properties on my entities, associations and properties using this post:
Extending Entity Framework 6 - adding custom properties to entities in designer
Now I need to use these custom properties when generating code in T4 but I have no clue how to access that information. Can someone point me in the right direction ?
regards,
Jurjen.
I've figured it out.
looking at, for instance, the entity variable in "foreach (var entity in typeMapper.GetItemsToGenerate(itemCollection))", this is a GlobalItem (https://msdn.microsoft.com/en-us/library/system.data.metadata.edm.globalitem(v=vs.110).aspx) wich contains MetadataProperties.
Listing these properties using a simple foreach
foreach( var mp in entity.MetadataProperties)
{
this.WriteLine("{0} = '{1}'", mp.Name, mp.Value);
}
results in a list
Name = 'Role'
NamespaceName = 'Model1'
Abstract = 'False'
...
http://saop.si:RecordTracked = '<a:RecordTracked xmlns:a="http://saop.si">true</a:RecordTracked>'
http://saop.si:DisplayMember = '<a:DisplayMember xmlns:a="http://saop.si">true</a:DisplayMember>'
as you can see, the custom properties (RecordTracked, DisplayName) are listed as well.
I have created 2 functions in within public class CodeStringGenerator to retrieve any custom property. Call it like this :
CodeStringGenerator.GetCustomPropertyAsBoolean(entity, "RecordTracked");
private bool GetCustomPropertyAsBoolean(GlobalItem item, string propertyName)
{
var _value = GetCustomProperty(item, propertyName);
if (string.IsNullOrEmpty(_value ))
{ return false; }
return _value.Equals("true", StringComparison.CurrentCultureIgnoreCase);
}
private string GetCustomProperty(GlobalItem item, string propertyName)
{
var _found = item.MetadataProperties.FirstOrDefault(p => p.Name.StartsWith("http://") &&
p.Name.EndsWith(propertyName, StringComparison.CurrentCultureIgnoreCase ));
if (_found == null)
{ return string.Empty; }
var _value = _found.Value as System.Xml.Linq.XElement;
if (_value == null)
{ return string.Empty; }
return _value.Value;
}
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.
Currently I am doing like this:
For Example:
public update(Person model)
{
// Here model is model return from form on post
var oldobj = db.Person.where(x=>x.ID = model.ID).SingleOrDefault();
db.Entry(oldobj).CurrentValues.SetValues(model);
}
It works, but for example,
I have 50 columns in my table but I displayed only 25 fields in my form (I need to partially update my table, with remaining 25 column retain same old value)
I know it can be achieve by "mapping columns one by one" or by creating "hidden fields for those remaining 25 columns".
Just wondering is there any elegant way to do this with less effort and optimal performance?
This is a very good question. By default I have found that as long as change tracking is enabled (it is by default unless you turn it off), Entity Framework will do a good job of applying to the database only what you ask it to change.
So if you only change 1 field against the object and then call SaveChanges(), EF will only update that 1 field when you call SaveChanges().
The problem here is that when you map a view model into an entity object, all of the values get overwritten. Here is my way of handling this:
In this example, you have a single entity called Person:
Person
======
Id - int
FirstName - varchar
Surname - varchar
Dob - smalldatetime
Now let's say we want to create a view model which will only update Dob, and leave all other fields exactly how they are, here is how I do that.
First, create a view model:
public class PersonDobVm
{
public int Id { get; set; }
public DateTime Dob { get; set; }
public void MapToModel(Person p)
{
p.Dob = Dob;
}
}
Now write the code roughly as follows (you'll have to alter it to match your context name etc):
DataContext db = new DataContext();
Person p = db.People.FirstOrDefault();
// you would have this posted in, but we are creating it here just for illustration
var vm = new PersonDobVm
{
Id = p.Id, // the Id you want to update
Dob = new DateTime(2015, 1, 1) // the new DOB for that row
};
vm.MapToModel(p);
db.SaveChanges();
The MapToModel method could be even more complicated and do all kinds of additional checks before assigning the view model fields to the entity object.
Anyway, the result when SaveChanges is called is the following SQL:
exec sp_executesql N'UPDATE [dbo].[Person]
SET [Dob] = #0
WHERE ([Id] = #1)
',N'#0 datetime2(7),#1 int',#0='2015-01-01 00:00:00',#1=1
So you can clearly see, Entity Framework has not attempted to update any other fields - just the Dob field.
I know in your example you want to avoid coding each assignment by hand, but I think this is the best way. You tuck it all away in your VM so it does not litter your main code, and this way you can cater for specific needs (i.e. composite types in there, data validation, etc). The other option is to use an AutoMapper, but I do not think they are safe. If you use an AutoMapper and spelt "Dob" as "Doob" in your VM, it would not map "Doob" to "Dob", nor would it tell you about it! It would fail silently, the user would think everything was ok, but the change would not be saved.
Whereas if you spelt "Dob" as "Doob" in your VM, the compiler will alert you that the MapToModel() is referencing "Dob" but you only have a property in your VM called "Doob".
I hope this helps you.
I swear by EntityFramework.Extended. Nuget Link
It lets you write:
db.Person
.Where(x => x.ID == model.ID)
.Update(p => new Person()
{
Name = newName,
EditCount = p.EditCount+1
});
Which is very clearly translated into SQL.
Please try this way
public update(Person model)
{
// Here model is model return from form on post
var oldobj = db.Person.where(x=>x.ID = model.ID).SingleOrDefault();
// Newly Inserted Code
var UpdatedObj = (Person) Entity.CheckUpdateObject(oldobj, model);
db.Entry(oldobj).CurrentValues.SetValues(UpdatedObj);
}
public static object CheckUpdateObject(object originalObj, object updateObj)
{
foreach (var property in updateObj.GetType().GetProperties())
{
if (property.GetValue(updateObj, null) == null)
{
property.SetValue(updateObj,originalObj.GetType().GetProperty(property.Name)
.GetValue(originalObj, null));
}
}
return updateObj;
}
I have solved my Issue by using FormCollection to list out used element in form, and only change those columns in database.
I have provided my code sample below; Great if it can help someone else
// Here
// collection = FormCollection from Post
// model = View Model for Person
var result = db.Person.Where(x => x.ID == model.ID).SingleOrDefault();
if (result != null)
{
List<string> formcollist = new List<string>();
foreach (var key in collection.ToArray<string>())
{
// Here apply your filter code to remove system properties if any
formcollist.Add(key);
}
foreach (var prop in result.GetType().GetProperties())
{
if( formcollist.Contains(prop.Name))
{
prop.SetValue(result, model.GetType().GetProperty(prop.Name).GetValue(model, null));
}
}
db.SaveChanges();
}
I still didn't find a nice solution for my problem, so I created a work around. When loading the Entity, I directly make a copy of it and name it entityInit. When saving the Entity, I compare the both to see, what really was changed. All the unchanged Properties, I set to unchanged and fill them with the Database-Values. This was necessary for my Entities without Tracking:
// load entity without tracking
var entityWithoutTracking = Context.Person.AsNoTracking().FirstOrDefault(x => x.ID == _entity.ID);
var entityInit = CopyEntity(entityWithoutTracking);
// do business logic and change entity
entityWithoutTracking.surname = newValue;
// for saving, find entity in context
var entity = Context.Person.FirstOrDefault(x => x.ID == _entity.ID);
var entry = Context.Entry(entity);
entry.CurrentValues.SetValues(entityWithoutTracking);
entry.State = EntityState.Modified;
// get List of all changed properties (in my case these are all existing properties, including those which shouldn't have changed)
var changedPropertiesList = entry.CurrentValues.PropertyNames.Where(x => entry.Property(x).IsModified).ToList();
foreach (var checkProperty in changedPropertiesList)
{
try
{
var p1 = entityWithoutTracking.GetType().GetProperty(checkProperty).GetValue(entityWithoutTracking);
var p2 = entityInit.GetType().GetProperty(checkProperty).GetValue(entityInit);
if ((p1 == null && p2 == null) || p1.Equals(p2))
{
entry.Property(checkProperty).CurrentValue = entry.Property(checkProperty).OriginalValue; // restore DB-Value
entry.Property(checkProperty).IsModified = false; // throws Exception for Primary Keys
}
} catch(Exception) { }
}
Context.SaveChanges(); // only surname will be updated
This is way I did it, assuming the new object has more columns to update that the one we want to keep.
if (theClass.ClassId == 0)
{
theClass.CreatedOn = DateTime.Now;
context.theClasses.Add(theClass);
}
else {
var currentClass = context.theClasses.Where(c => c.ClassId == theClass.ClassId)
.Select(c => new TheClasses {
CreatedOn = c.CreatedOn
// Add here others fields you want to keep as the original record
}).FirstOrDefault();
theClass.CreatedOn = currentClass.CreatedOn;
// The new class will replace the current, all fields
context.theClasses.Add(theClass);
context.Entry(theClass).State = EntityState.Modified;
}
context.SaveChanges();
In EF you can do like this
var result = db.Person.Where(x => x.ID == model.ID).FirstOrDefault();
if(result != null){
result.Name = newName;
result.DOB = newDOB;
db.Person.Update(result);
}
Or you can use
using (var db= new MyDbContext())
{
var result= db.Person.Where(x => x.ID == model.ID).FirstOrDefault();
result.Name= newName;
result.DOB = newDOB;
db.Update(result);
db.SaveChanges();
}
For more detail please EntityFramework Core - Update Only One Field
No Worry guys
Just write raw sql query
db.Database.ExecuteSqlCommand("Update Person set Name='"+_entity.Name+"' where Id = " + _entity.ID + "");
In EF code first, one specifies field properties and relationships using the fluent interface. This builds up a model. Is it possible to get a reference to this model, and reflect on it?
I want to be able to retrieve for a given field, if it is required, what its datatype is, what length, etc...
You need to access the MetadataWorkspace. The API is pretty cryptic. You may want to replace DataSpace.CSpace with DataSpace.SSpace to get the database metadata.
public class MyContext : DbContext
{
public void Test()
{
var objectContext = ((IObjectContextAdapter)this).ObjectContext;
var mdw = objectContext.MetadataWorkspace;
var items = mdw.GetItems<EntityType>(DataSpace.CSpace);
foreach (var i in items)
{
foreach (var member in i.Members)
{
var prop = member as EdmProperty;
if (prop != null)
{
}
}
}
}
How do I convert a datatable into a POCO object in Asp.Net MVC?
Pass each DataRow into the class constructor (or use getters/setters) and translate each column into the corresponding property. Be careful with nullable columns to extract them properly.
public class POCO
{
public int ID { get; set; }
public string Name { get; set; }
public DateTime? Modified { get; set; }
...
public POCO() { }
public POCO( DataRow row )
{
this.ID = (int)row["id"];
this.Name = (string)row["name"];
if (!(row["modified"] is DBNull))
{
this.Modified = (DateTime)row["modified"];
}
...
}
}
A data table typically holds many rows - do you want to convert each row into an object instance?
In that case, you could e.g. add a constructor to your POCO object that will accept a DataRow as parameter, and then extracts the bits and pieces from that DataRow:
public YourPOCO(DataRow row)
{
this.Field1 = row["Field1"].ToString();
...
this.FieldN = Convert.ToInt32(row["FieldN"]);
}
and so on, and then call that constructor on each of the rows in the DataTable.Rows collection:
List<YourPOCO> list = new List<YourPOCO>();
foreach(DataRow row in YourDataTable.Rows)
{
list.Add(new YourPOCO(row));
}
And you could then create a ASP.NET MVC view or partial view based on this "YourPOCO" type and use the "List" template to create a list of "YourPOCO" instances in a list-like display.
Marc
Old question, anyway this can be usefull for somebody:
private static T CreatePocoObject<T>(DataRow dr) where T : class, new()
{
try
{
T oClass = new T();
Type tClass = typeof (T);
MemberInfo[] methods = tClass.GetMethods();
ArrayList aMethods = new ArrayList();
object[] aoParam = new object[1];
//Get simple SET methods
foreach (MethodInfo method in methods)
{
if (method.DeclaringType == tClass && method.Name.StartsWith("set_"))
aMethods.Add(method);
}
//Invoke each set method with mapped value
for (int i = 0; i < aMethods.Count; i++)
{
try
{
MethodInfo mInvoke = (MethodInfo)aMethods[i];
//Remove "set_" from method name
string sColumn = mInvoke.Name.Remove(0, 4);
//If row contains value for method...
if (dr.Table.Columns.Contains(sColumn))
{
//Get the parameter (always one for a set property)
ParameterInfo[] api = mInvoke.GetParameters();
ParameterInfo pi = api[0];
//Convert value to parameter type
aoParam[0] = Convert.ChangeType(dr[sColumn], pi.ParameterType);
//Invoke the method
mInvoke.Invoke(oClass, aoParam);
}
}
catch
{
System.Diagnostics.Debug.Assert(false, "SetValuesToObject failed to set a value to an object");
}
}
return oClass;
}
catch
{
System.Diagnostics.Debug.Assert(false, "SetValuesToObject failed to create an object");
}
return null;
}
Source is http://blog.developers.ie/cgreen/archive/2007/09/14/using-reflection-to-copy-a-datarow-to-a-class.aspx
I saw your other question about using a datatable in the data access layer. If you return POCO at some point its a good idea to let your DAL return POCO already.
You would use an SqlDataReader to fill the POCO. This is more light weight. Sometimes its easier to use DataSet and DataTable for Lists of entries, but if you tranform the rows into stronly typed POCOS anyway I am pretty shure that this is the way to go.
I have an entityframework entity called "ABC" (attributes ID and Title).
On update record view, I have added the ID as hidden field and title is the text box.
Controller looks like something:
public ActionResult UpdateAction( ABC obj )
I get everything fine and fair in obj - i.e., the title, and the ID.
Now to update the record in database, I read the original entity:
var original = (from x in base.context.ABC where x.id == obj.id ).Single();
Now to reflect the changes in original, I think should do the update model:
this.TryUpdateModel( original );
I get an error :| ... stating that column ID cannot be changed.
The property 'id' is part of the object's key information and cannot be modified.
I do not want to manually assign the properties back to original object.
The other alternative can be:
TryUpdateModel(original, new string[] { "Title" }, form.ToValueProvider());
But I hate strings - also, my object has like 20 attributes :|
Can someone please suggest a better pattern of doing so?
Rgds
public class ControllerExt : Controller
{
protected void UpdateModel<TModel>(TModel model, params Expression<Func<TModel, object>>[] property) where TModel : class
{
var props = new List<string>(property.Length);
foreach (var p in property)
{
var memberExpression = RemoveUnary(p.Body) as MemberExpression;
if (memberExpression == null)
{
throw new NullReferenceException("Can not retrieve info about member of {0}".FormatThis(typeof(TModel).Name));
}
props.Add(memberExpression.Member.Name);
}
this.UpdateModel(model, props.ToArray());
}
private static Expression RemoveUnary(Expression body)
{
var unary = body as UnaryExpression;
if (unary != null)
{
return unary.Operand;
}
return body;
}
}
Example:
UpdateModel<MyModel>(model, x => x.PropertyFromMyModel_1, x => x.PropertyFromMyModel_2);