I'm thinking of building some generic extensions that will take a way all these null, throw checks and asserts and instead use fluent APIs to handle this.
So I'm thinking of doing something like this.
Shall() - Not quite sure about this one yet
.Test(...) - Determines whether the contained logic executed without any errors
.Guard(...) - Guards the contained logic from throwing any exception
.Assert(...) - Asserts before the execution of the code
.Throw(...) - Throws an exception based on a certain condition
.Assume(...) - Similar to assert but calls to Contract.Assume
Usage: father.Shall().Guard(f => f.Shop())
The thing is that I don't want these extra calls at run-time and I know AOP can solve this for me, I want to inline these calls directly to the caller, if you have a better way of doing that please do tell.
Now, before I'm researching or doing anything I wonder whether someone already done that or know of a tool that is doing it ?
I really want to build something like that and release it to public because I think that it can save a lot of time and headache.
Some examples.
DbSet<TEntity> set = Set<TEntity>();
if (set != null)
{
if (Contains(entity))
{
set.Remove(entity);
}
else
{
set.Attach(entity);
set.Remove(entity);
}
}
Changes to the following.
Set<TEntity>().Shall().Guard(set =>
{
if (Contains(entity))
{
set.Remove(entity);
}
else
{
set.Attach(entity);
set.Remove(entity);
}
});
Instead of being funny and try to make fun of other people, some people can really learn something about maturity, you can share your experience and tell me what's so good or bad about it, that I'll accept.
I'm not trying to recreate Code Contracts, I know what it is I'm using it everyday, I'm trying to move the boilerplate code that is written to one place.
Sometimes you have methods that for each call you have to check the returned object and is not your code so you can't ensure that the callee won't result a null so in the caller you have to perform null checks on the returned object so I thought of something that may allow me to perform these checks easily when chaining calls.
Update: I'll have to think about it some more and change the API to make the intentions clear and the code more readable.
I think that the idea is not polished at all and that indeed I went too far with all these methods.
Anyways, I'll leave it for now.
It sounds like you're describing something like Code Contracts: http://msdn.microsoft.com/en-us/devlabs/dd491992
If I understand what you're looking for, then the closest thing I've come up with is the extension method:
public static Chain<T>(this T obj, Action<T> act)
{
act(obj);
return obj;
}
This allows you to do the following:
Set.Remove(Set.FirstOrDefault(entity) ?? entity.Chain(a => Set.Add(a)));
As you can see, though, this isn't the most readable code. This isn't to say that Chain extension method is bad (and it certainly has its uses), but that Chain extension method can definitely be abused, so use cautiously or the ghost of programming past will come back to haunt you.
Related
I've been trying to approach this issue for a while now and I have not been able to find an answer.
Basically, I have a certain method that, when called, actually executes another different method rather than the method itself which I assume needs me to modify to where the method's pointer is pointing.
Say this,
public class A : OtherRandomClass
{
protected void SomeMethod()
{
//code
}
}
public class B
{
public void OtherMethod()
{
//code that I want to execute when SomeMethod is called
}
}
I cannot modify class A's source unfortunately, but what I want to try to do is to make any calls to SomeMethod actually invoke OtherMethod while preventing SomeMethod itself from being invoked, I don't want to resort to swapping method bodies.
I am aware of just how much bad practice this is, but the framework I'm using is just plain stupid and I have no other choice.
Any approaches to this?
Edit: Found what I was looking for, thanks to anyone who attempted to help!
This doesn't look simple, and to be perfectly honest, I never attempted to do such a thing.
I'd really like to know your context, because if what you want to do was my last option, I would not work with this assembly.
This answer suggests replacing the loaded method body (which is written then in Intermediate Language) with your own, by using reflection:
You can use MethodInfo.GetMethodBody().GetILAsByteArray(), modify
that, and then plug it back into MethodBuilder.CreateMethodBody().
You can then check this question and its answers to have a rough idea of how you should implement it all, but it looks like CreateMethodBody isn't fully supported and could have some unexpected behavior.
Overall, it's pretty complicated and doesn't look worth the hassle.
With the move to EF6.1, our goal is to use exclusivity the Async/Await options speaking with our data sets. While porting from our previous Linq2Sql, there are many .ToList(), .FirstOrDefault(), and .Count()'s. I know we can search and fix those all, but it would be nice if we could, at compile time, prevent those functions from even being permitted into a build. Does anyone have have a creative idea on how to accomplish this? Even if they were compiler warnings that could be thrown (such as use of the Obsolete attribute).
You can use the .NET Compiler Platform to write a Diagnostic and Code Fix that will look for these patterns and provide warnings/errors.
You could even implement a Syntax Transformation to automatically change these constructs - though the effort might be more expensive than just doing it by hand.
Following up to this... i never found a solution that can detect this at compile time, but I was able to do this in code in the DataContext:
public EfMyCustomContext(string connctionString)
: base(string.Format(CONNECTION_STRING, connctionString))
{
#if DEBUG
this.Database.Log = LogDataBaseCall;
#endif
}
#if DEBUG
private void LogDataBaseCall(string s)
{
if (s.Contains("Executing "))
{
if (!s.Contains("asynchronously"))
{
// This code was not executed asynchronously
// Please look at the stack trace, and identify what needs
// to be loaded. Note, an entity.SomeOtherEntityOrCollection can be loaded
// with the eConnect API call entity.SomeOtherEntityOrCollectionLoadAsync() before using the
// object that is going to hit the sub object. This is the most common mistake
// and this breakpoint will help you identify all synchronous code.
// eConnect does not want any synchronous code in the code base.
System.Diagnostics.Debugger.Break();
}
}
}
#endif
Hope this helps someone else, and still would love if there was some option during compile.
I have a piece of software written with fluent syntax. The method chain has a definitive "ending", before which nothing useful is actually done in the code (think NBuilder, or Linq-to-SQL's query generation not actually hitting the database until we iterate over our objects with, say, ToList()).
The problem I am having is there is confusion among other developers about proper usage of the code. They are neglecting to call the "ending" method (thus never actually "doing anything")!
I am interested in enforcing the usage of the return value of some of my methods so that we can never "end the chain" without calling that "Finalize()" or "Save()" method that actually does the work.
Consider the following code:
//The "factory" class the user will be dealing with
public class FluentClass
{
//The entry point for this software
public IntermediateClass<T> Init<T>()
{
return new IntermediateClass<T>();
}
}
//The class that actually does the work
public class IntermediateClass<T>
{
private List<T> _values;
//The user cannot call this constructor
internal IntermediateClass<T>()
{
_values = new List<T>();
}
//Once generated, they can call "setup" methods such as this
public IntermediateClass<T> With(T value)
{
var instance = new IntermediateClass<T>() { _values = _values };
instance._values.Add(value);
return instance;
}
//Picture "lazy loading" - you have to call this method to
//actually do anything worthwhile
public void Save()
{
var itemCount = _values.Count();
. . . //save to database, write a log, do some real work
}
}
As you can see, proper usage of this code would be something like:
new FluentClass().Init<int>().With(-1).With(300).With(42).Save();
The problem is that people are using it this way (thinking it achieves the same as the above):
new FluentClass().Init<int>().With(-1).With(300).With(42);
So pervasive is this problem that, with entirely good intentions, another developer once actually changed the name of the "Init" method to indicate that THAT method was doing the "real work" of the software.
Logic errors like these are very difficult to spot, and, of course, it compiles, because it is perfectly acceptable to call a method with a return value and just "pretend" it returns void. Visual Studio doesn't care if you do this; your software will still compile and run (although in some cases I believe it throws a warning). This is a great feature to have, of course. Imagine a simple "InsertToDatabase" method that returns the ID of the new row as an integer - it is easy to see that there are some cases where we need that ID, and some cases where we could do without it.
In the case of this piece of software, there is definitively never any reason to eschew that "Save" function at the end of the method chain. It is a very specialized utility, and the only gain comes from the final step.
I want somebody's software to fail at the compiler level if they call "With()" and not "Save()".
It seems like an impossible task by traditional means - but that's why I come to you guys. Is there an Attribute I can use to prevent a method from being "cast to void" or some such?
Note: The alternate way of achieving this goal that has already been suggested to me is writing a suite of unit tests to enforce this rule, and using something like http://www.testdriven.net to bind them to the compiler. This is an acceptable solution, but I am hoping for something more elegant.
I don't know of a way to enforce this at a compiler level. It's often requested for objects which implement IDisposable as well, but isn't really enforceable.
One potential option which can help, however, is to set up your class, in DEBUG only, to have a finalizer that logs/throws/etc. if Save() was never called. This can help you discover these runtime problems while debugging instead of relying on searching the code, etc.
However, make sure that, in release mode, this is not used, as it will incur a performance overhead since the addition of an unnecessary finalizer is very bad on GC performance.
You could require specific methods to use a callback like so:
new FluentClass().Init<int>(x =>
{
x.Save(y =>
{
y.With(-1),
y.With(300)
});
});
The with method returns some specific object, and the only way to get that object is by calling x.Save(), which itself has a callback that lets you set up your indeterminate number of with statements. So the init takes something like this:
public T Init<T>(Func<MyInitInputType, MySaveResultType> initSetup)
I can think of three a few solutions, not ideal.
AIUI what you want is a function which is called when the temporary variable goes out of scope (as in, when it becomes available for garbage collection, but will probably not be garbage collected for some time yet). (See: The difference between a destructor and a finalizer?) This hypothetical function would say "if you've constructed a query in this object but not called save, produce an error". C++/CLI calls this RAII, and in C++/CLI there is a concept of a "destructor" when the object isn't used any more, and a "finaliser" which is called when it's finally garbage collected. Very confusingly, C# has only a so-called destructor, but this is only called by the garbage collector (it would be valid for the framework to call it earlier, as if it were partially cleaning the object immediately, but AFAIK it doesn't do anything like that). So what you would like is a C++/CLI destructor. Unfortunately, AIUI this maps onto the concept of IDisposable, which exposes a dispose() method which can be called when a C++/CLI destructor would be called, or when the C# destructor is called -- but AIUI you still have to call "dispose" manually, which defeats the point?
Refactor the interface slightly to convey the concept more accurately. Call the init function something like "prepareQuery" or "AAA" or "initRememberToCallSaveOrThisWontDoAnything". (The last is an exaggeration, but it might be necessary to make the point).
This is more of a social problem than a technical problem. The interface should make it easy to do the right thing, but programmers do have to know how to use code! Get all the programmers together. Explain simply once-and-for-all this simple fact. If necessary have them all sign a piece of paper saying they understand, and if they wilfully continue to write code which doesn't do anythign they're worse than useless to the company and will be fired.
Fiddle with the way the operators are chained, eg. have each of the intermediateClass functions assemble an aggregate intermediateclass object containing all of the parameters (you mostly do it this was already (?)) but require an init-like function of the original class to take that as an argument, rather than have them chained after it, and then you can have save and the other functions return two different class types (with essentially the same contents), and have init only accept a class of the correct type.
The fact that it's still a problem suggests that either your coworkers need a helpful reminder, or they're rather sub-par, or the interface wasn't very clear (perhaps its perfectly good, but the author didn't realise it wouldn't be clear if you only used it in passing rather than getting to know it), or you yourself have misunderstood the situation. A technical solution would be good, but you should probably think about why the problem occurred and how to communicate more clearly, probably asking someone senior's input.
After great deliberation and trial and error, it turns out that throwing an exception from the Finalize() method was not going to work for me. Apparently, you simply can't do that; the exception gets eaten up, because garbage collection operates non-deterministically. I was unable to get the software to call Dispose() automatically from the destructor either. Jack V.'s comment explains this well; here was the link he posted, for redundancy/emphasis:
The difference between a destructor and a finalizer?
Changing the syntax to use a callback was a clever way to make the behavior foolproof, but the agreed-upon syntax was fixed, and I had to work with it. Our company is all about fluent method chains. I was also a fan of the "out parameter" solution to be honest, but again, the bottom line is the method signatures simply could not change.
Helpful information about my particular problem includes the fact that my software is only ever to be run as part of a suite of unit tests - so efficiency is not a problem.
What I ended up doing was use Mono.Cecil to Reflect upon the Calling Assembly (the code calling into my software). Note that System.Reflection was insufficient for my purposes, because it cannot pinpoint method references, but I still needed(?) to use it to get the "calling assembly" itself (Mono.Cecil remains underdocumented, so it's possible I just need to get more familiar with it in order to do away with System.Reflection altogether; that remains to be seen....)
I placed the Mono.Cecil code in the Init() method, and the structure now looks something like:
public IntermediateClass<T> Init<T>()
{
ValidateUsage(Assembly.GetCallingAssembly());
return new IntermediateClass<T>();
}
void ValidateUsage(Assembly assembly)
{
// 1) Use Mono.Cecil to inspect the codebase inside the assembly
var assemblyLocation = assembly.CodeBase.Replace("file:///", "");
var monoCecilAssembly = AssemblyFactory.GetAssembly(assemblyLocation);
// 2) Retrieve the list of Instructions in the calling method
var methods = monoCecilAssembly.Modules...Types...Methods...Instructions
// (It's a little more complicated than that...
// if anybody would like more specific information on how I got this,
// let me know... I just didn't want to clutter up this post)
// 3) Those instructions refer to OpCodes and Operands....
// Defining "invalid method" as a method that calls "Init" but not "Save"
var methodCallingInit = method.Body.Instructions.Any
(instruction => instruction.OpCode.Name.Equals("callvirt")
&& instruction.Operand is IMethodReference
&& instruction.Operand.ToString.Equals(INITMETHODSIGNATURE);
var methodNotCallingSave = !method.Body.Instructions.Any
(instruction => instruction.OpCode.Name.Equals("callvirt")
&& instruction.Operand is IMethodReference
&& instruction.Operand.ToString.Equals(SAVEMETHODSIGNATURE);
var methodInvalid = methodCallingInit && methodNotCallingSave;
// Note: this is partially pseudocode;
// It doesn't 100% faithfully represent either Mono.Cecil's syntax or my own
// There are actually a lot of annoying casts involved, omitted for sanity
// 4) Obviously, if the method is invalid, throw
if (methodInvalid)
{
throw new Exception(String.Format("Bad developer! BAD! {0}", method.Name));
}
}
Trust me, the actual code is even uglier looking than my pseudocode.... :-)
But Mono.Cecil just might be my new favorite toy.
I now have a method that refuses to be run its main body unless the calling code "promises" to also call a second method afterwards. It's like a strange kind of code contract. I'm actually thinking about making this generic and reusable. Would any of you have a use for such a thing? Say, if it were an attribute?
What if you made it so Init and With don't return objects of type FluentClass? Have them return, e.g., UninitializedFluentClass which wraps a FluentClass object. Then calling .Save(0 on the UnitializedFluentClass object calls it on the wrapped FluentClass object and returns it. If they don't call Save they don't get a FluentClass object.
In Debug mode beside implementing IDisposable you can setup a timer that will throw a exception after 1 second if the resultmethod has not been called.
Use an out parameter! All the outs must be used.
Edit: I am not sure of it will help, tho...
It would break the fluent syntax.
I have a simple question for you (i hope) :)
I have pretty much always used void as a "return" type when doing CRUD operations on data.
Eg. Consider this code:
public void Insert(IAuctionItem item) {
if (item == null) {
AuctionLogger.LogException(new ArgumentNullException("item is null"));
}
_dataStore.DataContext.AuctionItems.InsertOnSubmit((AuctionItem)item);
_dataStore.DataContext.SubmitChanges();
}
and then considen this code:
public bool Insert(IAuctionItem item) {
if (item == null) {
AuctionLogger.LogException(new ArgumentNullException("item is null"));
}
_dataStore.DataContext.AuctionItems.InsertOnSubmit((AuctionItem)item);
_dataStore.DataContext.SubmitChanges();
return true;
}
It actually just comes down to whether you should notify that something was inserted (and went well) or not ?
I typically go with the first option there.
Given your code, if something goes wrong with the insert there will be an Exception thrown.
Since you have no try/catch block around the Data Access code, the calling code will have to handle that Exception...thus it will know both if and why it failed. If you just returned true/false, the calling code will have no idea why there was a failure (it may or may not care).
I think it would make more sense if in the case where "item == null" that you returned "false". That would indicate that it was a case that you expect to happen not infrequently, and that therefore you don't want it to raise an exception but the calling code could handle the "false" return value.
As it standards, you'll return "true" or there'll be an exception - that doesn't really help you much.
Don't fight the framework you happen to be in. If you are writing C code, where return values are the most common mechanism for communicating errors (for lack of a better built in construct), then use that.
.NET base class libraries use Exceptions to communicate errors and their absence means everything is okay. Because almost all code uses the BCL, much of it will be written to expect exceptions, except when it gets to a library written as if C# was C with no support for Exceptions, each invocation will need to be wrapped in a if(!myObject.DoSomething){ System.Writeline("Damn");} block.
For the next developer to use your code (which could be you after a few years when you've forgotten how you originally did it), it will be a pain to start writing all the calling code to take advantage of having error conditions passed as return values, as changes to values in an output parameter, as custom events, as callbacks, as messages to queue or any of the other imaginable ways to communicate failure or lack thereof.
I think it depends. Imaging that your user want to add a new post onto a forum. And the adding fail by some reason, then if you don't tell the user, they will never know that something wrong. The best way is to throw another exception with a nice message for them
And if it does not relate to the user, and you already logged it out to database log, you shouldn't care about return or not any more
I think it is a good idea to notify the user if the operation went well or not. Regardless how much you test your code and try to think out of the box, it is most likely that during its existence the software will encounter a problem you did not cater for, thus making it behave incorrectly. The use of notifications, to my opinion, allow the user to take action, a sort of Plan B if you like when the program fails. This action can either be a simple work around or else, inform people from the IT department so that they can fix it.
I'd rather click that extra "OK" button than learn that something went wrong when it is too late.
You should stick with void, if you need more data - use variables for it, as either you'll need specific data (And it can be more than one number/string) and an excpetion mechanism is a good solution for handling errors.
so.. if you want to know how many rows affected, if a sp returned something ect... - a return type will limit you..
I have a couple of methods that return a bool depending on their success, is there anything wrong with calling those methods inside of the IF() ?
//&& makes sure that Method2() will only get called if Method1() returned true, use & to call both methods
if(Method1() && Method2())
{
// do stuff if both methods returned TRUE
}
Method2() doesn't need to fire if Method1() returns FALSE.
Let me know there's any problem with the code above.
thank you.
EDIT: since there was nothing wrong with the code, I'll accept the most informative answer ... added the comment to solve the "newbie & &&" issue
I'll throw in that you can use the & operator (as opposed to &&) to guarantee that both methods are called even if the left-hand side is false, if for some reason in the future you wish to avoid short-circuiting.
The inverse works for the | operator, where even if the left-hand condition evaluates to true, the right-hand condition will be evaluated as well.
No, there is nothing wrong with method calls in the if condition. Actually, that can be a great way to make your code more readable!
For instance, it's a lot cleaner to write:
private bool AllActive()
{
return x.IsActive && y.IsActive && z.IsActive;
}
if(AllActive())
{
//do stuff
}
than:
if(x.IsActive && y.IsActive && z.IsActive)
{
//do stuff
}
As useful as they are, sequence points can be confusing. Unless you really understand that, it is not clear that Method2() might not get called at all. If on the other hand you needed BOTH methods to be called AND they had to return true, what would you write? You could go with
bool result1 = Method1();
bool result2 = Method2();
if (result1 && result2)
{
}
or you could go with
if (Method1())
if (Method2())
{
}
So I guess the answer to you question IMHO is, no, it's not exactly clear what you mean even though the behavior will be what you describe.
I would only recommend it if the methods are pure (side-effect-free) functions.
While, as everyone says, there's nothing "wrong" with doing things this way, and in many cases you're doing precisely what the language was designed for.
Bear in mind, however, that for maintainabilities sake, if Method2 has side effects (that is, it changes somethings state) it may not be obvious that this function is not being called (a good programmer will usually know, but even good programmers sometimes have brain farts).
If the short circuited expression has some kind of side effect, it may be more readable to seperate the statements, strictly from a maintenance perspective.
Looks good to me, multiple clauses in the if() block will short circuit if an earlier condition fails.
There shouldn't be any problem.
The normal behavior is that Method1() will execute, and if that returns true Method2() will execute, and depending on what Method2() returns, you may / may not enter the if() statement.
Now, this assumes that the compiler generates code that executes that way. If you want to be absolutely sure that Method2() doesn't execute unless Method1() returns true you could write it like this
if( Method1() )
{
if( Method2() )
{
// do stuff if both methods returned TRUE
}
}
But, I've always observed that your code will run as expected, so this is probably not necessary.
Nothin' wrong.
Actually...I wouldn't name them Method1 and Method2. Something more descriptive. Maybe passive sounding too (like StuffHasHappened or DataHasLoaded)
Looks good to me, but there are some caveats... This is NOT the kind of thing where blanket rules apply.
My guidelines are:
If the method names are short, and there are not too many of them, then it's all good.
If you have too many statements/method calls inside the if statement, you most likely are comparing more than one "set" of things. Break those "sets" out and introduce temporary variables.
"Too many" is subjective, but usually more than around 3
When I say "method names are short" I'm talking not just about the names, but the parameters they take as well. Basically the effort required for someone to read it. For example if( Open(host) ) is shorter than if( WeCouldConnectToTheServer ). The total size of all these items is what it comes down to.
Personally, I would consider
if(Method1() && Method2())
{
// do stuff if both methods returned TRUE
}
to be a bad practice. Yes, it works in the current environment, but so does
if(Method1())
{
if (Method2())
{
// do stuff if both methods returned TRUE
}
}
But will it work in ALL environments? Will future, possibly non-Microsoft, C# compilers work this way? What if your next job involves another language where both methods will always be called? I wouldn't rely on that particular construct not because it's wrong, but because it doesn't solve any serious problem, and it may become wrong in the future