I have an object in C# with lets say 20 properties and it's part of a datacontract. I also have another business entity with similar properties, which I want to populate from the response object. Is there any way to do this other than assigning each property of one object to the corresponding properties of the other?
Yes, take a look at Automapper
MiscUtil has an answer to this (PropertyCopy) that uses Expression (.NET 3.5) and a static field to cache the compiled delegate (so there is negligible cost per invoke):
DestType clone = PropertyCopy<DestType>.CopyFrom(original);
If you are using 2.0, then probably reflection would be your friend. You can use HyperDescriptor to improve the performance if you need.
Reflection is an option if you want to do it in an automated manner, provided the property names are easily mappable between the objects.
Automapper is worth a try, but in the end, I decided it wasn't for me. The big problem with those sorts of tools is you incur a great deal of runtime overhead each and every time a mapping occurs. I asked this same question last week and I ended up rolling my own solution (look at the accepted answer). You're free to modify the source I provided, I make no claims as to it's effectiveness, suitability, performance, you-break-it-you-get-to-keep-the-pieces, etc., but it works well enough for me to create design time object to object mapping.
C# Object Clone Wars might be a good starting point.
Related
I find it a recurring inconvenience that a lot of simple types in the .Net framework are not marked as serializable. For example: System.Drawing.Point or Rectangle.
Both those structs only consist of primitive data and should be serializable in any format easily. However, because of the missing [System.Serializable] attribute, I can't use them with a BinaryFormatter.
Is there any reason for this, which I'm not seeing?
It is simply a question of efficiency. Tagging a field as serializable the compiler must map each field onto a table of aliases. If they were all marked as serializables every object injecting or inheriting them need to be mapped aswell onto the table of aliases to process its serialization when probably you will never use them and it has a cost of memory and processing and it is more unsafe. Test it with millions of elements and you will see.
Personally, I believe it has less to do with the need to pass the buck, and more to do with the fact of usefulness and actual use, coupled with the fact that the .NET Framework is simply that, a framework. It is designed to be a stepping stone which provides you the basics to complete tasks that would otherwise be daunting in other languages, rather than do everything for you.
There really isn't anything stopping you from creating your own serialization mechanisms and extensions which provide the functionality you're seeking, or relying on many of the other products out there which are FOSS or paid which achieve this for you OOB.
Granted, #Hans Passant's answer is I think very close to the truth, there's a lot of other facets to this which go beyond just simply "It's not my problem." You can take it whatever way you want, but the ultimate thing you need to get out of it is, "where can I go from here?"
A webservice I use (I have no control over it) returns an XML string, which I convert to an XDcoument and then create a list of objects of a particular type:
private static List<ProductDetail> productList(XmlDocument _xDoc) {
XDocument xdoc = XDocument.Load(new XmlNodeReader(_xDoc));
var pList = from p in xdoc.Root.Elements("DataRow")
select new ProductDetail
{
Product = (string)p.Element("Product"),
ProductDesc = (string)p.Element("ProductDesc"),
ExtraKey = (string)p.Element("ExtraKey"),
SalesGroup = (string)p.Element("SalesGroup"),
Donation = (string)p.Element("Donation"),
Subscription = (string)p.Element("Subscription"),
StockItem = (string)p.Element("StockItem"),
MinimumQuantity = (string)p.Element("MinimumQuantity"),
MaximumQuantity = (string)p.Element("MaximumQuantity"),
ProductVATCategory = (string)p.Element("ProductVATCategory"),
DespatchMethod = (string)p.Element("DespatchMethod"),
SalesDescription = (string)p.Element("SalesDescription"),
HistoryOnly = (string)p.Element("HistoryOnly"),
Warehouse = (string)p.Element("Warehouse"),
LastStockCount = (string)p.Element("LastStockCount"),
UsesProductNumbers = (string)p.Element("UsesProductNumbers"),
SalesQuantity = (string)p.Element("SalesQuantity"),
AmendedBy = (string)p.Element("AmendedBy")
};
return pList.ToList();
}
This works fine and is very fast. However it means I have to maintain this code separately from the model if it changes and I was just wondering if there was a shortcut to avoid me having to specify each individual field as I'm doing? I already have a class for ProductDetail so is there some way of using that at the object level? I've a feeling that the answer may be "yes, but using reflection" which will probably have a negative impact on the process speed so is not something I'd be keen on.
There is another option that I can think of (beyond the two you already talked about in your question.. i.e. Manual mapping and Reflection based approach.
Dynamic Methods
It is DynamicMethod (The MSDN link has example as well)
This approach can give you best of both worlds.. i.e.
Performance
Dynamic
But the catch is, you trade it off with
Increased code complexity
Reduced debug ability.
It can be thought of as hybrid of the two, in the sense, it is can be as flexible / dynamic as you'd like it to be (effort will also vary accordingly), and yet hold the performance benefits similar to manually mapped objects (your sample code above).
With this approach, there is a one time cost of initializing your DynamicMethod at appropriate time (application startup / first use etc).. and then cache it for subsequent use. If you need the mapper only a handful number of times.. then it can be much less useful.. But I am assuming that is not the case for your scenario.
Technique I'd recommend
You'd notice from the example, that creating a DynamicMethod involves emitting IL op-codes at runtime (and reflection as well), and that can look very complex and difficult task, because it is more complex code and harder to debug. However, what I tend to do in this situation, is write the method I'd like to emit using DynamicMethod by hand (you already have that), and then study IL generated for that method by the compiler.
In other words, you don't have to be a master at writing IL by hand.. If you are not already familiar how to write IL for a given scenario, just write it up in plain C# as you imagine it.. compile it, and then use ILDASM to figure out how you want to emit similar IL for your DynamicMethod.
Other Options - Deserializers
For the sake of completeness, I'd say the problem you are trying to solve is in general that of deserializing XML payload into plain objects POCOs. It is not very clear from the question if you even considered them, and excluded them as an option, or they weren't even considered.
If you didn't even look in that direction, you can start with what is already available in .Net - DataContractSerializer. There can be other implementations which you may be able to find on the internet.. which may suit your needs.
The reasons why they may not be a good fit for your scenario (if I understand it right) could be -
Deserializers tend to be generic in functionality, and hence certainly not the same level of performance as code you have above.
May be there is a deserializer out there which uses DynamicMethod for performance, but I have never seen one. Also note that different implementations can obviously have different performance characteristics
The data may not lend itself for easy use with common / famous deserializers.
Like if the XML you have is deeply nested, and you want to map properties / element at different levels without creating complex object hierarchy. (One might now argue that such problems can be solved with XSL transforms.)
The implementation may not have the features you may really need.
Like what if the object to which data needs to be mapped is of Generic Type.
Conclusion
Manual mapping is fastest, but least flexible.
Reflection will certainly be slow, but can provide higher flexibility.
DynamicMethod (part of System.Reflection.Emit namespace) can give you most flexibility and performance (assuming high use with cached instance), if you are willing to pay the price of even higher complexity and development effort.
Deserializers give you varying degree of flexibility and performance, but are not always suitable.
EDIT: Realized, that for completeness, some more options could be added to the list.
T4 templates - Also hard to develop (IMHO) and debug / troubleshoot (Depends on complexity of what you are trying to achieve with them. I had to debug them by installing a VS add-in, and debug by attaching one Visual Studio instance as debugee from another Visual Studio instance as debugger - ugly. May be there are better ways, but I'd avoid them). Manual action may still be required to refresh generated code. (There is a good possibility that it can be automated during build, but I have never tried it)
Code generation - You write custom code generation tool, and hook it as a pre-build step in appropriate projects. (You could do this code generation as part of build, or in theory, also after your application is deployed and runs the first time, but for this scenario, build time generation should be more suitable.)
Background:
I have 2 instances of an object of the same type. One object is populated with the configuration of a device I'm connected to, the other object is populated with a version of the configuration that I've stored on my hard drive.
The user can alter either, so I'd like to compare them and present the differences to the user.
Each object contains a number of ViewModel properties, all of which extend ViewModelBase, which are the ones I want to compare.
Question:
Is a better way to do this than what I'm about to propose.
I'm thinking of using Reflection to inspect each property in my objects, and for each that extend ViewModelBase, I'll loop through each of those properties. For any that are different, I'll put the name and value into a list and then present that to the user.
Rather than inventing this wheel, I'm wondering if this is this a problem that's been solved before? Is there a better way for it to be done?
Depending on the amount of properties to be compared, manual checking would be the more efficient option. However, if you have lots of properties or want the check to be dynamic (i.e. you just add new properties and it automagically works), then I think Reflection is the way to go here.
Why not just implement the equals operator for your type?
http://msdn.microsoft.com/en-us/library/ms173147(v=vs.80).aspx
Edit: Having read more carefully I see what you're actually asking is what the most efficient way of doing the actual comparison is.
Doing it via reflection saves on code but is slower. Doing it with lots of manual comparions is fairly quick but more code.
If you are fairly determent and lazy in the good way. You can mix benefits of both solutions. With help of tool like cci you can emit method that compares properties. The beauty of this is that your reflection code will be executed on compile time leaving you with strait forward method to execute at runtime. This allows you to change models as you see fit and not worry about comparison code. There is a down side to this and that is learning cci which is quite challenging.
I'm about to build a search page on a website and the search is going to be extensive with a couple of models and with each model having a lot of properties.
Is there a way to do this in a generic way or use reflector as I have seen in some posts? I need some pointers or tips on how to aproach this. Highly appreciate it.
You can use reflection to get the information you need. If you have a type T you can use
typeof(T).GetProperties()
to get all public properties. Same is possible for fields, methods, ... If you need more meta data to generate your search, you can use attributes to annotate the properties (or fields, methods, ...) That's the way I would get started. Further details depend on your exact use case.
Can you give more details?
What is the purpose of your search? Give me the 30 second version so I can understand where you are going with this.
Are you planning on using RegEx and word stemming?
What kinds of values count as matches?
I assume you only want to search properties on the objects/models. Right?
Do want to see every property or only some of them?
What kinds of data is stored in the properties? (string, byte[], enum, etc)
Brainstorming Ideas:
What about searching one the DB server-side instead of in your hydrated objects? It might be faster (at run-time) to leverage your DB than load all of the objects into memory then reflect upon them.
You could also write a method that supports your search within the context of the model itself. You pass in the search rule set as an expression then find the match. If you have some kind of a collection container, the search could be run at that level against all of the objects in the collection.
If you want some reflection code, I wrote something that shows a lot of info about an object via reflection. I wrote this a long while ago (Dec 2009). I'm not sure if it does what you want. Take a look. If it works for you, use it! (Link)
I am fairly new to reflection and I would like to know, if possible, how to create an instance of a class then add properties to the class, set those properties, then read them later. I don't have any code as i don't even know how to start going about this. C# or VB is fine.
Thank You
EDIT: (to elaborate)
My system has a dynamic form creator. one of my associates requires that the form data be accessible via web service. My idea was to create a class (based on the dynamic form) add properties to the class (based on the forms fields) set those properties (based on the values input for those fields) then return the class in the web service.
additionally, the web service will be able to set the properties in the class and eventually commit those changes to the db.
If you mean dynamically create a class, then the two options are:
Reflection.Emit - Difficult, Fast to create the class
CodeDom - Less Difficult, Slower to create the class
If you mean create an instance of an existing class, then start with Activator.CreateInstance to create an instance of the object, and then look at the methods on Type such as GetProperty which will return a PropertyInfo that you can call GetValue and SetValue on.
Update: For the scenario you describe, returning dynamic data from a web service, then I'd recommend against this approach as it's hard for you to code, and hard for statically-typed languages to consume. Instead, as suggested in the comments and one of the other answers, some sort of dictionary would likely be a better option.
(Note that when I say return some sort of dictionary, I am speaking figuratively rather than literally, i.e. return something which is conceptually the same as a dictionary such as a list of key-value pairs. I wouldn't recommend directly returning one (even if you're using WCF which does support this) because it's typically better to have full control over the XML you return.)
I know this is being overly simplified by why not just KISS and generate the required Xml to return through the Web Service and then parse the returned Xml to populate the database.
My reasoning is that for the expanded reason you suggest doing this I can see the value or reason for wanting a dynamic class?
The Execution-Time Code Generation chapter of Eric Gunnerson's book (A Programmer's Introduction to C#) has some great information on this topic. See page 14 and onwards in particular. He outlines the two main methods of accomplishing dynamic class/code generation (CodeDOM and the Reflection.Emit namespace). It also discusses the difficulty and performance of the two approaches. Have a read through that, and you ought to find everything you might need.
The real question is, what do you need to use those properties for?
What are gonna be the use cases? Do you need to bind those properties to the UI somehow? Using what kind of technology? (WPF, Windows Forms?)
Is it just that you need to gather a set of key/value pairs at runtime? Then maybe a simple dictionary would do the trick.
Please elaborate if you can on what it is you need, and I'm sure people here can come up with plenty of ways to help you, but it's difficult to give a good answer without more context.