I'm only using Code Analysis for cleaning, organizing and ensuring these changes are globally performed for all instances of a particular warning. I'm down to the final, and it's CA2227.
CA2227 Collection properties should be read only Change '' to be
read-only by removing the property setter.
Note this is for mapping of EDI documents. These classes are to represent a whole or part of an EDI document.
public class PO1Loop
{
public SegmentTypes.PO1LoopSegmentTypes.PO1 PO1 { get; set; }
public Collection<SegmentTypes.PO1LoopSegmentTypes.PID1> PIDRepeat1 { get; set; }
public Collection<SegmentTypes.PO1LoopSegmentTypes.PID2> PIDRepeat2 { get; set; }
public SegmentTypes.PO1LoopSegmentTypes.PO4 PO4 { get; set; }
/* Max Use: 8 */
public Collection<SegmentTypes.PO1LoopSegmentTypes.ACK> ACKRepeat { get; set; }
}
You can see all of the Collection properties will give me this warning, and there are hundreds of them. When using the above class I instantiate it without any data. Then externally I add the data and set each individual variable through its public accessor. I do not instantiate this class with all the data prepared and passed using a constructor method (IMO for the size these can reach it can easily wreak havoc on the eyes). When complete and all properties are assigned the class as a whole is then used to generate that part of a document it represents.
My question is, for the usage described above, what would be a better approach for setting this up correctly? Do I keep the public accessors and suppress this warning entirely, or is there a entirely different solution that would work?
Here's what MSDN says about the error, and also how you can avoid it.
Here's my take on the issue.
Consider, the following class:
class BigDataClass
{
public List<string> Data { get; set; }
}
This class will throw that exact same issue. Why? Because Collections do not need a setter. Now, we can do anything with that object: assign Data to an arbitrary List<string>, add elements to Data, remove elements from Data, etc. If we remove the setter, we only lose the ability to directly assign to that property.
Consider the following code:
class BigDataClass
{
private List<string> data = new List<string>();
public List<string> Data { get { return data; } } // note, we removed the setter
}
var bigData = new BigDataClass();
bigData.Data.Add("Some String");
This code is perfectly valid and in fact the recommended way to do things. Why? Because the List<string> is a reference to a memory location, that contains the remainder of the data.
Now, the only thing you cannot now do with this, is directly set the Data property. I.e. the following is invalid:
var bigData = new BigDataClass();
bigData.Data = new List<string>();
This is not necessarily a bad thing. You'll notice that on many .NET types this model is used. It's the basics of immutability. You usually do not want direct access to the mutability of Collections, as this can cause some accidental behavior that has strange issues. This is why Microsoft recommends you omit setters.
Example:
var bigData = new BigDataClass();
bigData.Data.Add("Some String");
var l2 = new List<string>();
l2.Add("String 1");
l2.Add("String 2");
bigData.Data = l2;
Console.WriteLine(bigData.Data[0]);
We might be expecting Some String, but we'll get String 1. This also means that you cannot reliably attach events to the Collection in question, so you cannot reliably determine if new values are added or values are removed.
A writable collection property allows a user to replace the collection with a completely different collection.
Essentially, if you only ever need to run the constructor, or assignment, once, then omit the set modifier. You won't need it, direct assignment of collections is against best-practices.
Now, I'm not saying never use a setter on a Collection, sometimes you may need one, but in general you should not use them.
You can always use .AddRange, .Clone, etc. on the Collections, you only lose the ability of direct assignment.
Serialization
Lastly, what do we do if we wish to Serialize or Deserialize a class that contains our Collection without a set? Well, there is always more than one way to do it, the simplest (in my opinion) is to create a property that represents the serialized collection.
Take our BigDataClass for example. If we wished to Serialize, and then Deserialize this class with the following code, the Data property would have no elements.
JavaScriptSerializer jss = new JavaScriptSerializer();
BigDataClass bdc = new BigDataClass();
bdc.Data.Add("Test String");
string serd = jss.Serialize(bdc);
Console.WriteLine(serd);
BigDataClass bdc2 = jss.Deserialize<BigDataClass>(serd);
So, to fix this, we can simply modify our BigDataClass a bit to make it use a new string property for Serialization purposes.
public class BigDataClass
{
private List<string> data = new List<string>();
[ScriptIgnore]
public List<string> Data { get { return data; } } // note, we removed the setter
public string SerializedData { get { JavaScriptSerializer jss = new JavaScriptSerializer(); return jss.Serialize(data); } set { JavaScriptSerializer jss = new JavaScriptSerializer(); data = jss.Deserialize<List<string>>(value); } }
}
Another option is always the DataContractSerializer (which is really a better option, in general.) You can find information about it on this StackOverflow question.
With current VS2019 we can simply do this:
public List<string> Data { get; } = new List<string>();
This satisfies CA2227 and can be serialized/deserialized.
The deserialization works because List<> has an "Add" method, and the serializer knows how to handle a read-only collection property with an Add method (the property is read-only but not the elements) (I use Json.Net, other serializers may behave differently).
Edit:
As pointed out it should be "=" and not "=>" (compiler will prevent you using "=>"). If we used "public List Data => new List();" then it would create a new list every time the property was accessed which is not what we want either.
Edit:
Note that this will NOT work if the type of the property is an interface, such as IList
Edit:
I think the handling of interfaces is determined by the serializer used. The following works perfectly. I'm sure all common serializers know how to handle ICollection. And if you have some custom interface that does not implement ICollection then you should be able to configure the serializer to handle it, but in that case CA2227 probably won't be triggered making it irrelevant here. (As it is a read-only property you have to assign a concrete value within the class so it should always be serializing and de-serializing a non-null value)
public class CA2227TestClass
{
public IList Data { get; } = new List<string>();
}
[TestMethod]
public void CA2227_Serialization()
{
var test = new CA2227TestClass()
{
Data = { "One", "Two", "Three" }
};
var json = JsonConvert.SerializeObject(test);
Assert.AreEqual("{\"Data\":[\"One\",\"Two\",\"Three\"]}", json);
var jsonObject = JsonConvert.DeserializeObject(json, typeof(CA2227TestClass)) as CA2227TestClass;
Assert.IsNotNull(jsonObject);
Assert.AreEqual(3, jsonObject.Data.Count);
Assert.AreEqual("One", jsonObject.Data[0]);
Assert.AreEqual("Two", jsonObject.Data[1]);
Assert.AreEqual("Three", jsonObject.Data[2]);
Assert.AreEqual(typeof(List<string>), jsonObject.Data.GetType());
}
💡 Alternative Solution 💡
In my situation, making the property read-only was not viable because the whole list (as a reference) could change to a new list.
I was able to resolve this warning by changing the properties' setter scope to be internal.
public List<Batch> Batches
{
get { return _Batches; }
internal set { _Batches = value; OnPropertyChanged(nameof(Batches)); }
}
Note one could also use private set...
The hint's (achilleas heal) of this warning seems really pointed to libraries for the documentation says (Bolding mine):
An externally visible writable property is a type that implements
System.Collections.ICollection.
For me it was, "Ok, I won't make it viewable externally...." and internal was fine for the app.
Thanks to #Matthew, #CraigW and #EBrown for helping me understanding the solution for this warning.
public class PO1Loop
{
public SegmentTypes.PO1LoopSegmentTypes.PO1 PO1 { get; set; }
public Collection<SegmentTypes.PO1LoopSegmentTypes.PID1> PIDRepeat1 { get; private set; }
public Collection<SegmentTypes.PO1LoopSegmentTypes.PID2> PIDRepeat2 { get; private set; }
public SegmentTypes.PO1LoopSegmentTypes.PO4 PO4 { get; set; }
/* Max Use: 8 */
public Collection<SegmentTypes.PO1LoopSegmentTypes.ACK> ACKRepeat { get; private set; }
public PO1Loop()
{
PIDRepeat1 = new Collection<SegmentTypes.PO1LoopSegmentTypes.PID1>();
PIDRepeat2 = new Collection<SegmentTypes.PO1LoopSegmentTypes.PID2>();
ACKRepeat = new Collection<SegmentTypes.PO1LoopSegmentTypes.ACK>();
}
}
When wanting to assign data to the collection types use AddRange, Clear or any other variation of method for modifying a collection.
Only while binding DTO, you need to suppress warnings.
otherwise a custom ModelBinder is required custom ModelBinder to bind collections.
quoting the rule documentation:
When to suppress warnings
You can suppress the warning if the property is part of a Data Transfer Object (DTO) class.
Otherwise, do not suppress warnings from this rule.
https://learn.microsoft.com/pt-br/visualstudio/code-quality/ca2227?view=vs-2019
DTOs often require serialization and deserialization. Thus, they are required to be mutable.
Having to create an alternate backing property is a pain.
Simply change the property type from List<string> to IReadOnlyList<string> then this works as expected without CA2227.
The collection is set via the property but you can also cast to List<string> if you wish to append or delete items.
class Holder
{
public IReadOnlyList<string> Col { get; set; } = new List<string>();
}
var list = new List<string> { "One", "Two" };
var holder = new Holder() { Col = list } ;
var json = JsonConvert.SerializeObject(holder);
// output json {"Col":["One","Two"]}
var deserializedHolder = JsonConvert.DeserializeObject<Holder>(json);
I had to fix some of the CA2227 violations, so i had to add the "readonly" keyword to the collection field and then of course, had to remove the setter property. Some code that have used the setter, just created a new collection object which initially was empty. This code sure did not compile so i had to add a SetXxx() method in order to realize the missing setter's functionality. I did it like this:
public void SetXxx(List<string> list)
{
this.theList.Clear();
this.theList.AddRange(list);
}
The code of callers using the setter has been replaced with a call to the method SetXxx().
Instead of creating a complete new list, the existing list now will be cleared and filled with new items from another list, passed in as a parameter. The original list, due to the fact it is readonly and created only once, will always remain.
I believe this is also a good way to avoid that the garbagae collector has to delete old objects that got out of scope and second, to create new collection objects although there is already one.
As an addition to Der Kommissar's excellent answer.
Starting with .NET 5 (C# 9.0) there are init-only properties. These properties are only settable under specific circumstances, see here for reference.
The following example should not raise a warning CA2227, yet still allow for the collection being set during object initialization.
using System.Collections.Generic;
namespace BookStore
{
public class BookModel
{
public ICollection<string> Chapters { get; init; }
}
}
Note that the current version of the .NET SDK still raises a warning when using the built-in analyzer (not the NuGet package). This is a known bug and should be fixed in the future.
To cover all the possible scenarios to resolve CA2227 error:
This covers the Entity relationship mapping when we use Entity Framework.
class Program
{
static void Main(string[] args)
{
ParentClass obj = new ParentClass();
obj.ChildDetails.Clear();
obj.ChildDetails.AddRange();
obj.LstNames.Clear();
obj.LstNames.AddRange();
}
}
public class ChildClass
{ }
public class ParentClass
{
private readonly ICollection<ChildClass> _ChildClass;
public ParentClass()
{
_ChildClass = new HashSet<ChildClass>();
}
public virtual ICollection<ChildClass> ChildDetails => _ChildClass;
public IList<string> LstNames => new List<string>();
}
I try to use Json.NET for consuming an OData (like) service. My data structures have collection properties.
However all those properties are wrapped in a property called 'results' by my service. Even the main query which returns with a collection of the entities are wrapped into a root property called results.
Although I am not an OData expert I think this is pretty much a standard because if I try to send an object graph for update, and omit this 'results' wrapper around say a int collection type property then I got an error message from the server "A collection was found without the 'results' property. In OData, each collection must be represented as a JSON object with a property 'results'"
So I understand the server error message, and I also know how to workaround this. Of course I can mimic this object graph in my C# object model, but after writing the 101st wrapper in my object model it tends to be boring, and I do not want to reinvent the wheel.
My question is there an out of the box solution how to deal with this result property, and make it transparent? If this is a 'standard' I suppose not I am the first who are facing this task.
Thanks in advance
you can just write one and use it everywhere
public class OData<T> where T : IEnumerable
{
public T results { get; set; }
}
public class X
{
public string Prop { get; set; }
public OData<List<int>> List { get; set; }
}
class Program
{
static void Main(string[] args)
{
var x = new X()
{
Prop = "test",
List = new OData<List<int>> {results = new List<int>() {1, 2, 3}}
};
Console.WriteLine(JsonConvert.SerializeObject(x));
}
}
I am attempting to save/load a class to an xml file that contains generic types using a DataContractSerializer. I have the save working, but have realized I can't load it because I don't have the list of knownTypes for the deserializer.
Is there a way of serializing/deserializing this class that would allow me to deserialize it without referencing any of the stored types directly?
Here is my SessionVariables class that I am trying to save/load:
[DataContract]
public class SessionVariables
{
[DataMember]
private Dictionary<Type, ISessionVariables> _sessionVariables = new Dictionary<Type, ISessionVariables>();
private object _syncLock = new object();
public T Get<T>()
where T : ISessionVariables, new()
{
lock (_syncLock)
{
ISessionVariables vars = null;
if (_sessionVariables.TryGetValue(typeof(T), out vars))
return (T)vars;
vars = new T();
_sessionVariables.Add(typeof(T), vars);
return (T)vars;
}
}
public IList<Type> GetKnownTypes()
{
IList<Type> knownTypes = new List<Type>();
knownTypes.Add(this.GetType().GetType()); // adds System.RuntimeType
foreach (Type t in _sessionVariables.Keys)
{
if (!knownTypes.Contains(t))
knownTypes.Add(t);
}
return knownTypes;
}
}
The different modules of the application extend the ISessionVariables interface to create their own set of session variables, like this:
[DataContract]
public class ModuleASessionVariables : ISessionVariables
{
[DataMember]
public string ModuleA_Property1{ get; set; }
[DataMember]
public string ModuleA_Property2 { get; set; }
}
[DataContract]
public class ModuleBSessionVariables : ISessionVariables
{
[DataMember]
public string ModuleB_Property1{ get; set; }
[DataMember]
public string ModuleB_Property2 { get; set; }
}
And a singleton instance of the SessionVariables class is used to access session variables, like this:
singletonSessionVariables.Get<ModuleASessionVariables>().ModuleA_Property1
singletonSessionVariables.Get<ModuleBSessionVariables>().ModuleB_Property2
I got the save working like this:
using (FileStream writer = new FileStream(#"C:\test.txt", FileMode.Create))
{
DataContractSerializer dcs = new DataContractSerializer(typeof(SessionVariables), singletonSessionVariables.GetKnownTypes());
dcs.WriteObject(writer, singletonSessionVariables);
writer.Close();
}
However this method does not work to deserialize the class because I don't know it's known types.
Can I serialize and deserialize generic types when I don't have direct library references to any of the types used? And if so, how?
The problem here is that you aren't just wanting to serialize data, but you also want to serialize data about your data, i.e., (cue the dramatic chipmunk) metadata.
That metadata, in this case, are the types of the models that held the data originally. Normally, this isn't an issue, but as you've discovered if you're taking advantage of polymorphism in your design, your single collection may contain two or more different types, each of which needs to be deserialized to their original type.
This is usually accomplished by saving this Type metadata to the serialized result. Different serialization methods does this in different ways. Xaml serialization uses xml namespaces associated with .net namespaces, then names the elements after the original type name. Json.net accomplishes this via a specific named value saved to the json object.
The default DataContractSerializer is not Type aware. Therefore you need to replace it with a version that understands the .NET Type system and can serialize/deserialize Type metadata to the resulting xml. Luckily, one already exists in the framework, the NetDataContractSerializer.
And that's how you pad a link-only answer. The Aristocrats.
You could accomplish this using a custom DataContractResolver. This allows you to plug into the deserialization pipeline and provide a type to deserialize into based upon the type/namespace that is found in the serialized graph.
Here's a good article on it:
http://blogs.msdn.com/b/carlosfigueira/archive/2011/09/21/wcf-extensibility-data-contract-resolver.aspx
IDesign has an implementation of a resolver that can be used for dynamic discovery of types on their site: http://idesign.net/Downloads/GetDownload/1848 (you will probably have to make some modifications to handle generics)
I have a curious case of this serialization issue - which has been asked many times on this site and I have gone through a few of these questions and tried the usual items to no avail:
Add [XmlInclude] to the class throwing the error
Remove namespaces
Add a different namespace to each class
To explain further, I have provided a simplified version of my code below. Essentially I am using a WebServiceHost object to run a RESTful service and one of my endpoints returns an object serialized as XML (I have annotated the object with [DataContract] and [DataMember] attributes). This object contains a SerializableDictionary<string, object> (here) where the value has been typed as object. I believe this is why it is failing:
Works fine when the value is assigned a primitive
When I assign a custom object to the KV pair V, I get the unexpected type exception probably because the Serializer does not know how to serilaize the object / some sort of namespacing issue
Obviously, I am unable to annotate Object.cs with [XmlInclude] and because it is a service and I am not myself serializing I cannot using something like
new Serializer(typeof(...), new Type[] { ... }}
Any idea's of what I can do? I thought about not typing the dict value as object and rtaher comething more concrete but the problem is that this value can take primitives or cusotm types. Some code to explain the above:
Edit: Updated the code below to make it more clear
[DataContract]
public class ResponseObject
{
[DataMember(Name = "data")]
public SerializableDictionary<string, object> Data { get;set; }
public ResponseObject()
{
Data = new SerializableDictionary<string, object>();
}
}
...
var d1 = new ResponseObject();
d1.Data.Add("some key", "some value"); //WORKS AND SERIALIZES PERFECLTY
var d2 = new ResponseObject();
d2.Data.Add("some other key", new SomeOtherObjecT());
var d3 = new ResponseObject();
d3.Data.Add("another key", d2); //THIS THROWS THE UNEXPECTED TYPE ERROR WHEN SEIRLAIZING SomeOtherObject
Edit: The error is thrown in SerializableDictionary where it is attempting to serialize an object of type ResponseObject. The two are in seperate projects - if that is significant?
Normally, you should add an [XmlInclude] to the ResponseObject class. In this case, it doesn't work because of the SerializableDictionary that you're using. That class creates another XmlSerializer in its implementation, and therefore it doesn't care about your [XmlInclude]'s. Basically it just cannot handle your use case. You should switch from the XmlSerializer to the DataContractSerializer which handles the Dictionary class and supports the [KnownType] attribute to register additional types: http://pastebin.com/vGLSaxHF . Also note that it's pointless to add [DataContract] and [DataMember] attributes in your current case because the XmlSerializer ignores those attributes, they are used by the DataContractSerializer only. Or if you're not sure how to change your serializer (I know I'm not) then you should either not be using a Dictionary or change the SerializableDictionary implementation to handle the dynamic object types that you want to use (find every line where it creates a new XmlSerializer). Or, as an alternative, define a base class for all your objects that you will ever put into the dictionary and do it like this:
[XmlInclude(typeof(Class1), XmlInclude(typeof(Class2)), etc]
public class AbstractBase { }
public class Class1 : AbstractBase { ... }
public class Class2 : AbstractBase { ... }
public class BigClass {
public SerializableDictionary<string, AbstractBase> Dictionary { get; set; }
}
This way, when the SerializableDictionary creates its own XmlSerializer, it will recognize the AbstractBase and from there, all of its descendants.
I'm trying to serialize into a Xml File an object which is declared as ILIst, but it's an instance of List. The exception tells me the reason: You can't serialize an interface.
This is really necessary in my design, or what other way do I have to serialize it?
You have to know what concrete type to instantiate.
The serializer has to go by the metadata, not runtime type. If all you knew was that your target object had to implement IList, what would you construct? There not necessarily even a class that implements it.
I suppose the reason you need to keep the design with IList is because it's a common interface to other module. One possible solution:
Instead of:
[XmlElement("Test")]
public IList<String> Tests
{
get;
set;
}
You can probably try:
[XmlElement("Test")]
public List<String> TestList
{
get;
set;
}
[XmlIgnore]
public IList<String> Tests
{
get { return TestList; }
}
This way you can keep the same interface, and meanwhile take advantage of serialize/deserialize functionality in .Net Xml library.
This should not be a problem, you can always use object.GetType(). Here's an example:
using System;
using System.Collections.Generic;
using System.Xml.Serialization;
class Program {
static void Main(string[] args) {
System.Collections.IList list = new List<int> { 1, 2, 3 };
var ser = new XmlSerializer(list.GetType());
ser.Serialize(Console.Out, list);
Console.ReadLine();
}
}
You can't serialize an interface because it doesn't contains any data. May be the best you can do is to implement ISerializable to control the serialization yourself.
I can see two options:
You can cast it back to List before when passing it to the serializer. Not ideal, but it would work.
You iterate over the IList and serialize each item to the same stream independently.