I am designing a web api where clients can retrieve information about a course.
In my model the entity course has several properties including the property instructor. Instructor is a class on it's own.
public class Course
{
public int Id { get; set; }
public string Title { get; set; }
public double? Duration { get; set; }
...
public Instructor Instructor { get; set; }
}
public class Instructor
{
public int Id { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public string Email { get; set; }
...
}
My question is, should i return all of the instructors properties when calling the course controller, set instructor to null or don't i retrun it at all?
Or are there any other options?
I have no idea what best practice is in this case. When the child entity is a collection i usualy just return an empty array. But in this case there is only 1 so i can't return an empty array.
best practice is to serialize that child entity, only if it's needed on client side when returned from this request. otherwise, you're just transferring unnecessary data.
to make the application decide whether or not to serialize it, (using Newtonsoft) you can implement a custom data contract resolver and use it when serializing your entities:
public class CustomDataContractResolver : DefaultContractResolver
{
protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
{
JsonProperty property = base.CreateProperty(member, memberSerialization);
if ((property.DeclaringType == typeof(Course) ||
property.DeclaringType.BaseType == typeof(Course)) &&
property.PropertyName == "Instructor")
{
property.ShouldSerialize =
instance =>
{
return true; // or false
};
}
return property;
}
}
Related
I have a quite big query in my WebApi which filters data from different models to send them in a DTO Object to FrontEnd(Angular).
I think DTO could be the right approach because it isn't neccessary for the frontend to get all parameters from all models.
My problem consists in from mapping the DTO Object back to my WebApi Models.
I tried Automapper from NugetPackages but it didn't work. I also heard that AutoMapper isn't the right choice when projects are getting bigger and bigger.
Below is the Code for my DTO object, query and models:
public class ApplicationSettingsDto
{
public string KeyName { get; set; }
public string Wert { get; set; }
public string DefaultValue { get; set; }
public string Description { get; set; }
}
Models:
public partial class ApplicationSettings
{
public string KeyName { get; set; }
public string Wert { get; set; }
public int Typ { get; set; }
public string DisplayOrder { get; set; }
}
public partial class ApplicationSettingsDefaults
{
public Guid Id { get; set; }
public string KeyName { get; set; }
public string Value { get; set; }
public int ProduktOption { get; set; }
}
public partial class Text
{
public string KeyName { get; set; }
public string Sprache { get; set; }
public string Text1 { get; set; }
public DateTime LetzteAenderung { get; set; }
}
Query:
public IQueryable Description()
{
int produktOption = GetProduktOption();
var query = from appl in _repositoryContext.ApplicationSettings
from text in _repositoryContext.Text
from defaults in _repositoryContext.ApplicationSettingsDefaults
//filter DefaultValues
where appl.KeyName.Equals(defaults.KeyName) &&
(defaults.ProduktOption.Equals(produktOption) || defaults.ProduktOption.Equals(65535))
//Filter TextValues
where EF.Functions.Like(text.KeyName, "%" + appl.KeyName) ||
EF.Functions.Like(text.KeyName, "%" + appl.KeyName + "$Descr")
where EF.Functions.Like(text.Sprache, "de-DE")
select new ApplicationSettingsDto()
{
KeyName = appl.KeyName,
Wert = appl.Wert,
DefaultValue = defaults.Value,
Description = text.Text1
}
into output orderby output.KeyName select output;
return query;
}
So this question is not about an detailed implementation, it's only about recommendations for implementing DTO because mapping can be a pain in the *ss, like in my example.
I'm open to new ideas or patterns I don't know yet to try to manage problems like this.
Thanks in Advance ;)
This question is likely to be closed as you have working code, but my recommendation, after years of having tried AutoMapper, reflection based mappings, and hand-written mappings, that you should just stick with what is simplest and works.
You typically have to write the mapping logic for your DTOs once. The code you would write is legible and straightforward. When you move that to AutoMapper, you now end up having an often unrelated and less legible piece of code for something very, very simple.
In the event that you need the mapping logic in another function, extract it to a separate method. In the event that you need it in a separate class, promote that mapping function to a static method on your DTO.
Most of my mapping code looks like:
// Some controller code
da.GetStudents().Select(Map); // Map is the function below
In the controller, the following method is defined:
public StudentDto Map(Student student)
{
if (student == null) return null;
return new StudentDto
{
FirstName = student.FirstName,
...
};
}
Hope that helps.
Here is a simplified version of my model:
public class User {
public int UserID { get; set; }
public string FirstName { get; set; }
public virtual ICollection<Recipe> Recipes { get; set; }
}
public class Recipe {
public int RecipeID { get; set; }
public string RecipeName { get; set; }
public int UserID { get; set; }
public virtual User User { get; set; }
}
I have a controller that I'd like to return a User as well as some summary information about their recipes. The scaffolded controller code looks like this:
var user = await _context.Users.SingleOrDefaultAsync(m => m.UserID == id);
It works fine. Now I try to add the Recipes, and it breaks:
var user = await _context.Users.Include(u => u.Recipes).SingleOrDefaultAsync(m => m.UserID == id);
My web browser starts to render the JSON, and it flickers and I get a message in the browser saying the connection has been reset.
My Theory - I believe that the parent (User) renders, which exposes the child (Recipe) which contains a reference to the parent (User), which contains a collection of the child (Recipe) and so on which is causing an infinite loop. Here's why I think this is happening:
The Visual Studio debugger allows me to navigate the properties in that way infinitely.
If I comment out the Recipe.User property, it works fine.
What I've tried
I tried to just include the data from Recipe that I need using Entity Framework projection (I'm attempting to not include Recipe.User). I tried to only include Recipe.RecipeName... but when I try to use projection to create an anonymous type like this:
var user = await _context.Users.Include(u => u.Recipes.Select(r => new { r.RecipeName })).SingleOrDefaultAsync(m => m.UserID == id);
I receive this error:
InvalidOperationException: The property expression 'u => {from Recipe r in u.Recipes select new <>f__AnonymousType1`1(RecipeName = [r].RecipeName)}' is not valid. The expression should represent a property access: 't => t.MyProperty'.
What is the solution? Can I project with different syntax? Am I going about this all wrong?
Consider using POCOs for serialization rather than doubly-linked entity classes:
public class UserPOCO {
public int UserID { get; set; }
public string FirstName { get; set; }
public ICollection<RecipePOCO> Recipes { get; set; }
}
public class RecipePOCO {
public int RecipeID { get; set; }
public string RecipeName { get; set; }
public int UserID { get; set; }
}
Copy the entity contents to the corresponding POCO and then return those POCO objects as the JSON result. The removal of the User property via usage of the RecipePOCO class will remove the circular reference.
I can propose you 3 options.
U sing [JsonIgnore] on property, but it will work on every use of Recipe class, so when you would like to just return Recipe class you won't have User in it.
public class Recipe {
public int RecipeID { get; set; }
public string RecipeName { get; set; }
public int UserID { get; set; }
[JsonIgnore]
public virtual User User { get; set; }
}
You can this solution to stop reference loop in all jsons https://stackoverflow.com/a/42522643/3355459
Last option is to create class (ViewModel) that will only have properties that you want send to the browser, and map your result to it. It is propably best from security reason.
I have been working on a shop site project, using asp.net core spa templates provided with the latest VS2017, and have come across an issue that I haven't had before, possibly because until now my apps were quite simple!
I know what the problem is and where, I just can't fix it. I have a product model which has a collection of "Attributes" and a collection of "Variations" (different colour size, etc) and those variations also have attributes, so if the same Attribute shows up in the Variation (VAttributes), as is already in the main "Attributes" I get the error
InvalidOperationException: The instance of entity type
'ProductAttribute' cannot be tracked because another instance with the
key value 'Id:2' is already being tracked. When attaching existing
entities, ensure that only one entity instance with a given key value
is attached.
The best answer I found was here : https://stackoverflow.com/a/19695833/6749293
Unfortunately, even with the above check I got the error, I even tried making a list of attached attributes, and if the vattribute matched one of the items in the list, I didn't attach it. In fact I found that even if I don't attach (_context.attach()) any of the vAttributes, it still throws the error!.
Here's the code in question:
public async Task<Product> Create(Product product)
{
try
{
foreach (var variation in product.Variations)
{
foreach (var vAttr in variation.VAttributes)
{
bool isDetached = _context.Entry(vAttr).State == EntityState.Detached;
if (isDetached)
_context.Attach(vAttr);
}
}
foreach (var attribute in product.Attributes)
{
bool isDetached = _context.Entry(attribute).State == EntityState.Detached;
if (isDetached)
_context.Attach(attribute);
}
foreach (var category in product.Categories)
{
_context.Attach(category);
_context.Attach(category).Collection(x => x.Children);
}
_context.Products.Add(product);
await Save();
return product;
}
catch (Exception)
{
throw;
}
}
The models for the 3 objects are as follows:
public class Product
{
[Key, DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
public int Id { get; set; }
public string Name { get; set; }
public decimal Price { get; set; }
public string Description { get; set; }
public string StockRef { get; set; }
public DateTime? LastModified { get; set; }
//image needed
public ICollection<ProductCategory> Categories { get; set; }
public ICollection<ProductAttribute> Attributes { get; set; }
public ICollection<ProductVariation> Variations { get; set; }
public Product()
{
Attributes = new List<ProductAttribute>();
Variations = new List<ProductVariation>();
Categories = new List<ProductCategory>();
}
}
Variation:
public class ProductVariation
{
[Key, DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
public int Id { get; set; }
public DateTime? LastModified { get; set; }
public virtual ICollection<ProductAttribute> VAttributes { get; set; }
//needs images
public decimal VPrice { get; set; }
public string VStockRef { get; set; }
}
Finally the Attribute:
public class ProductAttribute
{
[DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
public int Id { get; set; }
public string Name { get; set; }
[ForeignKey("AttributeCategory")]
public int AttributeCategoryId { get; set; }
public virtual AttributeCategory AttributeCategory { get; set; }
}
Most help I found when searching was more related to having repo's injected as singletons, or HttpPut methods where the code had check for existence omitting the .AsNoTracking() or it was a mistake that they had the second instance in some way, where I am aware of the second instance, I just don't know how to prevent it from being tracked!
EDIT: I found that adding a foreign key on the ProductVariation model to the Product that was being created failed as it was only a temp key!? anyway removed it from the variation model, so have updated my code. Also thought I'd add one of my earler failed attempts, that led to all of the foreach loops.
_context.AttachRange(product.Attributes);
_context.AttachRange(product.Categories);
_context.AttachRange(product.Variations);
_context.Add(product);
I believe you can allow EF to handle the tracking.
public virtual bool Create(T item)
{
try
{
_context.Add(item);
_context.SaveChanges();
return true;
}
catch (Exception e)
{
return false;
}
}
This allows for you to save the entire object structure without worring about attaching items.
var newProduct = new Product();
newProduct.Categories.Add(cat);
newProduct.Attributes.Add(att);
newProduct.Variations.Add(vari);
Create(newProduct);
I have build a .Net Mvc 4 application and now I want to extend it with REST.
I am using the Entity Framework and I have the following problem.
My goal is to have a system where categories have a number of products and where products can belong to multiple categories.
As follows:
public class Categorie
{
[Key]
public int Id { get; set; }
[Required]
public string Naam { get; set; }
[Required]
public string Omschrijving { get; set; }
public byte[] Plaatje { get; set; }
private List<Product> producten;
public virtual List<Product> Producten
{
get { return producten; }
set { producten = value; }
}
}
public class Product
{
[Key]
public int Id { get; set; }
[Required]
public string Naam { get; set; }
[Required]
public string Omschrijving { get; set; }
[Required]
public double Prijs { get; set; }
private List<Categorie> categorien = new List<Categorie>();
public virtual List<Categorie> Categorien
{
get { return categorien; }
set { categorien = value; }
}
[Required]
public byte[] Plaatje { get; set; }
}
NOTE: There are virtual properties in there so that my entity framework creates a merging table. Normally it links all the categorie's to the products and vice versa.
And my rest looks like:
// GET api/Rest/5
public Product GetProduct(int id)
{
Product product = db.Producten.Find(id);
Product newProduct = new Product();
if (product == null)
{
throw new HttpResponseException(Request.CreateResponse(HttpStatusCode.NotFound));
}
else
{
product.Categorien = null;
}
newProduct.Id = product.Id;
newProduct.Naam = product.Naam;
newProduct.Omschrijving = product.Omschrijving;
newProduct.Plaatje = product.Plaatje;
newProduct.Prijs = product.Prijs;
newProduct.Categorien = product.Categorien;
return newProduct;
}
First problem: I cannot send any product aslong as it has a categorie. I have to make it null.
Second problem: I cannot send the original product because of the first problem.
I am assuming your problem is with a circular reference during serialization, since categories reference multiple products and products reference multiple categories. One solution is to use Data Transfer Objects (DTO) instead of returning the straight entities you are using for EF. To make it easy to map your entities to the DTO's I would use AutoMapper. This is essentially what you are doing when you create an instance of newProduct in your REST API method, but AutoMapper takes the hard coding and drudgery out of mapping. Your DTO for a product would look very similar but they would not have the virtual navigation properties or the attributes needed by EF. A DTO for a product would look something like this.
public class Categorie
{
public int Id { get; set; }
public string Naam { get; set; }
public string Omschrijving { get; set; }
public byte[] Plaatje { get; set; }
}
public class Product
{
public int Id { get; set; }
public string Naam { get; set; }
public string Omschrijving { get; set; }
public double Prijs { get; set; }
public List<Categorie> categorien = new List<Categorie>();
public List<Categorie> Categorien
{
get { return categorien; }
set { categorien = value; }
}
public byte[] Plaatje { get; set; }
}
Notice that the DTO for Categorie does not contain a list of products, since in this case you want a listing of products. If you keep the field names the same for your DTO's as your entities AutoMapper will handle the mapping automatically. I usually keep the same class name for the DTO's and just distinguish them from the entities by having a different namespace. Your REST API method would look something like this.
// GET api/Rest/5
public Product GetProduct(int id)
{
Product product = db.Producten.Find(id);
return Mapper.Map<Product, Dto.Product>(product);
}
I keep coming across an i18n requirement where my data (not my UI) needs to be internationalized.
public class FooEntity
{
public long Id { get; set; }
public string Code { get; set; } // Some values might not need i18n
public string Name { get; set } // but e.g. this needs internationalized
public string Description { get; set; } // and this too
}
What are some approaches I could use?
Some things I've tried:-
1) Store a resource key in the db
public class FooEntity
{
...
public string NameKey { get; set; }
public string DescriptionKey { get; set; }
}
Pros: No need for complicated queries to get a translated entity. System.Globalization handles fallbacks for you.
Cons: Translations can't easily be managed by an admin user (have to deploy resource files whenever my Foos change).
2) Use a LocalizableString entity type
public class FooEntity
{
...
public int NameId { get; set; }
public virtual LocalizableString Name { get; set; }
public int NameId { get; set; }
public virtual LocalizableString Description { get; set; }
}
public class LocalizableString
{
public int Id { get; set; }
public ICollection<LocalizedString> LocalizedStrings { get; set; }
}
public class LocalizedString
{
public int Id { get; set; }
public int ParentId { get; set; }
public virtual LocalizableString Parent { get; set; }
public int LanguageId { get; set; }
public virtual Language Language { get; set; }
public string Value { get; set; }
}
public class Language
{
public int Id { get; set; }
public string Name { get; set; }
public string CultureCode { get; set; }
}
Pros: All localised strings in the same table. Validation can be performed per-string.
Cons: Queries are horrid. Have to .Include the LocalizedStrings table once for each localizable string on the parent entity. Fallbacks are hard and involve extensive joining. Haven't found a way to avoid N+1 when retrieving e.g. data for a table.
3) Use a parent entity with all the invariant properties and child entities containing all the localized properties
public class FooEntity
{
...
public ICollection<FooTranslation> Translations { get; set; }
}
public class FooTranslation
{
public long Id { get; set; }
public int ParentId { get; set; }
public virtual FooEntity Parent { get; set; }
public int LanguageId { get; set; }
public virtual Language Language { get; set; }
public string Name { get; set }
public string Description { get; set; }
}
public class Language
{
public int Id { get; set; }
public string Name { get; set; }
public string CultureCode { get; set; }
}
Pros: Not as hard (but still too hard!) to get a full translation of an entity into memory.
Cons: Double the number of entities. Can't handle partial translations of an entity - especially the case where, say, Name is coming from es but Description is coming from es-AR.
I have three requirements for a solution
Users can edit entities, languages, and translations at runtime
Users can supply partial translations with missing strings coming from a fallback as per System.Globalization
Entities can be brought into memory without running into e.g. N+1 issues
Why don't you take the best of both worlds?
Have a CustomResourceManager that handles the loading of resources and picking the right culture and use a CustomResourceReader that uses whatever backing store you like. A basic implementation could look like this, relying on convention of the Resourceky being Typename_PropertyName_PropertyValue. If for some reason the structure of the backingstore(csv/excel/mssql/table structure) need to change you only have the change the implementation of the ResourceReader.
As an added bonus I also got the real/transparent proxy going.
ResourceManager
class MyRM:ResourceManager
{
readonly Dictionary<CultureInfo, ResourceSet> sets = new Dictionary<CultureInfo, ResourceSet>();
public void UnCache(CultureInfo ci)
{
sets.Remove(ci):
}
protected override ResourceSet InternalGetResourceSet(CultureInfo culture, bool createIfNotExists, bool tryParents)
{
ResourceSet set;
if (!sets.TryGetValue(culture, out set))
{
IResourceReader rdr = new MyRR(culture);
set = new ResourceSet(rdr);
sets.Add(culture,set);
}
return set;
}
// sets Localized values on properties
public T GetEntity<T>(T obj)
{
var entityType = typeof(T);
foreach (var prop in entityType.GetProperties(
BindingFlags.Instance
| BindingFlags.Public)
.Where(p => p.PropertyType == typeof(string)
&& p.CanWrite
&& p.CanRead))
{
// FooEntity_Name_(content of Name field)
var key = String.Format("{0}_{1}_{2}",
entityType.Name,
prop.Name,
prop.GetValue(obj,null));
var val = GetString(key);
// only set if a value was found
if (!String.IsNullOrEmpty(val))
{
prop.SetValue(obj, val, null);
}
}
return obj;
}
}
ResourceReader
class MyRR:IResourceReader
{
private readonly Dictionary<string, string> _dict;
public MyRR(CultureInfo ci)
{
_dict = new Dictionary<string, string>();
// get from some storage (here a hardcoded Dictionary)
// You have to be able to deliver a IDictionaryEnumerator
switch (ci.Name)
{
case "nl-NL":
_dict.Add("FooEntity_Name_Dutch", "nederlands");
_dict.Add("FooEntity_Name_German", "duits");
break;
case "en-US":
_dict.Add("FooEntity_Name_Dutch", "The Netherlands");
break;
case "en":
_dict.Add("FooEntity_Name_Dutch", "undutchables");
_dict.Add("FooEntity_Name_German", "german");
break;
case "": // invariant
_dict.Add("FooEntity_Name_Dutch", "dutch");
_dict.Add("FooEntity_Name_German", "german?");
break;
default:
Trace.WriteLine(ci.Name+" has no resources");
break;
}
}
public System.Collections.IDictionaryEnumerator GetEnumerator()
{
return _dict.GetEnumerator();
}
// left out not implemented interface members
}
Usage
var rm = new MyRM();
var f = new FooEntity();
f.Name = "Dutch";
var fl = rm.GetEntity(f);
Console.WriteLine(f.Name);
Thread.CurrentThread.CurrentUICulture = new CultureInfo("nl-NL");
f.Name = "Dutch";
var dl = rm.GetEntity(f);
Console.WriteLine(f.Name);
RealProxy
public class Localizer<T>: RealProxy
{
MyRM rm = new MyRM();
private T obj;
public Localizer(T o)
: base(typeof(T))
{
obj = o;
}
public override IMessage Invoke(IMessage msg)
{
var meth = msg.Properties["__MethodName"].ToString();
var bf = BindingFlags.Public | BindingFlags.Instance ;
if (meth.StartsWith("set_"))
{
meth = meth.Substring(4);
bf |= BindingFlags.SetProperty;
}
if (meth.StartsWith("get_"))
{
// get the value...
meth = meth.Substring(4);
var key = String.Format("{0}_{1}_{2}",
typeof (T).Name,
meth,
typeof (T).GetProperty(meth, BindingFlags.Public | BindingFlags.Instance
|BindingFlags.GetProperty).
GetValue(obj, null));
// but use it for a localized lookup (rm is the ResourceManager)
var val = rm.GetString(key);
// return the localized value
return new ReturnMessage(val, null, 0, null, null);
}
var args = new object[0];
if (msg.Properties["__Args"] != null)
{
args = (object[]) msg.Properties["__Args"];
}
var res = typeof (T).InvokeMember(meth,
bf
, null, obj, args);
return new ReturnMessage(res, null, 0, null, null);
}
}
Real/Transparent proxy usage
var f = new FooEntity();
f.Name = "Dutch";
var l = new Localizer<FooEntity>(f);
var fp = (FooEntity) l.GetTransparentProxy();
fp.Name = "Dutch"; // notice you can use the proxy as is,
// it updates the actual FooEntity
var localizedValue = fp.Name;
First one is worthy if you have static content in database. For example if you have categories that relatively are not going to be changed by user. You can change them at next deploy. I do not like this solution personally. I do not consider this as a nice solution. This is just an escape of the problem.
Second one is the best but can cause a problem when you have two or more localizable fields in one entity. You can simplify it a bit and hard code languages on it like this
public class LocalizedString
{
public int Id { get; set; }
public string EnglishText { get; set; }
public string ItalianText { get; set; }
public string ArmenianText { get; set; }
}
Third one is not a good one neither. From this structure I can't be sure that all nodes (literals, lines, strings etc.) translated in specific culture.
Do not generalize too much. Each problem is kind of specialized and it needs specialized solution too. Too much generalization makes unjustified issues.