CQLinq Features

This document assumes that you are familiar with the C# LINQ syntax. Before reading the current document, it is preferable that you've read the CQLinq syntax document, but it is not mandatory, because when needed, some links to the CQLinq syntax document are proposed.

Once you've analyzed your first .NET code base with NDepend, you'll see that the NDepend project created contains around 200 default CQLinq queries and rules, categorized in different groups.

This set of default queries and rules cover the various CQLinq features in terms of code querying.

This document is a quick list of these features and informs the reader about what is possible with CQLinq. Keep in mind that these features are available through the well-defined list of types supported by the CQLinq querying model.


Querying the Code Object Model

The Code Elements Hierarchy
For NDepend, a .NET code base ICodeBase object is made of IAssembly, INamespace, IType, IMethod and IField objects. This object model reflects the hierarchical organization of the code where the code base is made of assemblies that contain namespaces that contain types that contain methods and fields. Notice that if a same namespace is spawned across N assemblies, the hierarchy is preserved and there are N INamespace objects, one contained in each assembly.

To navigate across this hierarchy, several parent and child properties are proposed like IMember.ParentType or IAssembly.ChildMethods. Most of the time, instead of using these properties it is more convenient to use the extension methods declared in the class ExtensionMethodsProjection that project a sequence of parent to a sequence of child and vice-versa. For example, see the usage of the extension method ChildMethods() in the query:
from m in Application.Namespaces.WithNameLike("ProductName.FeatureA").ChildMethods()
where m.CyclomaticComplexity > 10 select m


The Predefined Domains
To access these various kind of code elements, CQLinq proposed different predefined domains Assemblies, Namespaces, Types, Methods, Fields, codeBase, Application, ThirdParty and JustMyCode. Before continuing, it is important to click the link above and understand these predefined domains and how they relate to the application, third-party and just-my-code views of the code base.


Interfaces
Several ways are proposed to access the interfaces implementations, they are summarized in this query:
// Accessing the property IType.IsInterface
let interfaces = ThirdParty.Types.Where(t => t.IsInterface)

// Accessing the extension method ExtensionMethodsSequenceUsage.ThatImplementAny() from t in JustMyCode.Types.ThatImplementAny(interfaces)

// Accessing the extension methods ExtensionMethodsCQLinqDependency.Implement() where t.Implement("System.IDisposable")
select new { 
  
t,
  
// Accessing the property IType.InterfacesImplemented (there is also IType.TypesThatImplementMe)   thirdPartyInterfaces = t.InterfacesImplemented.Intersect(interfaces ) }

Base and Derived Classes Hierarchy
The same way there are several ways to navigate across the base and derived classes hierarchy:
// Accessing the extension method ExtensionMethodsSequenceUsage.ThatDeriveFromAny()
from t in JustMyCode.Types.ThatDeriveFromAny(ThirdParty.Types)

// Accessing the extension methods ExtensionMethodsCQLinqDependency.DeriveFrom() where !t.DeriveFrom("System.MulticastDelegate")
select new { 
 
t,
 
// Various properties of IType  t.BaseClass,
 
t.BaseClasses,
 
t.DerivedTypes, // Include direct and indirect derived types
 t.DirectDerivedTypes }

Methods abstract, virtual and override
The API proposes also facilities to navigate across methods overridden, and overrides:
from m in Application.Methods
where !m.IsAbstract && m.IsVirtual
select new { 
  
m,
  
// Enumerates methods overridden by m
  m.OverriddensBase,
  
// Enumerates methods that overrides m directly
  m.OverridesDirectDerived,
  
// Enumerates methods that overrides m directly or indirectly
  m.OverridesDerived }

Encapsulation and Visibility
Several facilities are proposed to deal with the visibility of a IMember object. Notice in the default query below the attributes that are related to visibility, and the possibility to obtain the optimal visibility. The optimal visibility is the most restricted visibility that a member can have in the context of the parent code base, without provoking a compilation syntax error. For example an internal method called only by methods defined in the same class could be declared as private.
// <Name>Methods that could have a lower visibility</Name>
warnif count > 0 from m in JustMyCode.Methods where 
  
m.Visibility != m.OptimalVisibility &&
  
!m.HasAttribute("NDepend.Attributes.CannotDecreaseVisibilityAttribute".AllowNoMatch()) &&
  
!m.HasAttribute("NDepend.Attributes.IsNotDeadCodeAttribute".AllowNoMatch()) &&
  
// If you don't want to link NDepend.API.dll you can use your own attributes and adapt this rule.
  
  
// Eliminate default constructor from the result.
  // Whatever the visibility of the declaring class,
  // default constructors are public and introduce noise
  // in the current rule.
  !( m.IsConstructor && m.IsPublic && m.NbParameters == 0) &&

  
// Don't decrease the visibility of Main() methods.
  !m.IsEntryPoint

select new { m, 
             
m.Visibility , 
             
CouldBeDeclared = m.OptimalVisibility,
             
m.MethodsCallingMe }

Attributes Tagging
The interface IAttributeTarget, implemented by IAssembly, IType, IMethod and IField, defines an attribute target. This interface is not implemented by INamespace, because a namespace cannot be tagged by an attribute.
The query below illustrates facilities proposed to browse attribute tagging.
from t in Types.TaggedWithAnyAttributes(
   
ThirdParty.Types.Where(t => t.IsAttributeClass))
where t.HasAttribute("System.SerializableAttribute")
select t
Notice that the property IType.IsAttributeClass is equivalent to DeriveFrom("System.Attribute").




Querying the Code Dependencies and Design

In the previous section, we have seen how to query different usages like interface implementation, class derivation, methods override and attributes tagging.

The NDepend code model proposes a general dependency model through the interfaces IUsed and IUser. With this two interfaces it is easy to browse dependency across any kind of code elements.

The dependency model is general in the sense that it doesn't rely on the kind of usage (interface implementation, field assignment, method call...). A and B being two code elements, we say that A depends on B if, when B is not available, A cannot be compiled.

Instead, of using methods of the IUsed and IUser interfaces, you'll often find more convenient to call extension methods from the class ExtensionMethodsCQLinqDependency where user and used code elements are named, like in the following query:
from m in Methods where 
m.IsUsing("System.IDisposable") && 
m.IsUsedBy("MyAssemblyName".AllowNoMatch()) 
select m
Notice how such extension methods are used by rules generated from dependency graph or dependency matrix, to forbid some particular dependency:
The rule generated is shown below. It could be easily adapted to forbid or enforce any dependency in a code base.
warnif count > 0 from a in Assemblies where 
a.IsUsing ("nunit.util") &&
(a.Name == @"nunit.uikit")
select new { a, a.NbLinesOfCode }
// the assembly nunit.uikit
// shouldn't use directly 
// the assembly nunit.util
// because (TODO insert your reason)

The extension methods of the class ExtensionMethodsSequenceUsage represent also a convenient way to query dependencies of a code base (and often a faster way as well):
from t in Types.UsedByAny(Types.Where(t => t.IsStatic)) select t

Each code element interfaces presents properties to get a sequence of user or used code elements (of the same kind). Here is a query relying on IMethod.MethodsCalled for example. Notes that in general, this facility is slower than the ones presented above.
let setters = Methods.Where(m => m.IsPropertySetter).ToHashSet()
from m in Methods
let settersCalled = m.MethodsCalled.Intersect(setters)
where settersCalled.Count() > 0
select new { m, settersCalled }

Indirect Usage
The class ExtensionMethodsCQLinqDependency presents some extension methods containing the word Indirect in their names, like for example, the extension method IsIndirectlyUsing(). These extension methods deal with indirect usage. For example if A is using B that is using C, A is not directly using C but A is indirectly using C (with a depth of 2). Here is a query that enumerates methods that are directly or indirectly calling the interface method System.IDisposable.Dispose().
from m in Methods 
let depth0 = m.IsIndirectlyUsing("System.IDisposable.Dispose()")
select m
The extension method DepthOfIsUsing goes further since it returns the depth of usage.
from m in Methods 
let depth0 = m.DepthOfIsUsing("System.IDisposable.Dispose()")
where depth0  >= 0 orderby depth0 ascending
select new { m, depth0 }
The depth returned is a Nullable<ushort> value.
  • It is null if m doesn't call indirectly the target method.
  • It is 1 if m calls directly the target method.
  • It is greater than 1 if m calls indirectly the target method.
This indirect usage possibility is especially useful to generate Call Graphs or Class Inheritance Graphs.

Some of the extension methods of the class ExtensionMethodsSequenceUsage also contain the word Indirect or the word Depth to work with indirect usage from a sequence to a code element or even any code elements of a target sequence (suffix Any). Such extension method named DepthOf... returns a ICodeMetric<TCodeElement,TNumeric> object. This code metric object represents the code metric that assigns the indirect usage depth (as defined above), to any code element of the input sequence. Code elements that are not in the ICodeMetric<,>.DefinitionDomain have a null depth.

For example, the following query matches all methods that are calling, directly or indirectly the setter of a property, with the depth of call:
let setters = Methods.Where(m => m.IsPropertySetter).ToHashSet()
let depthMetric = Application.Methods.DepthOfIsUsingAny(setters)
from m in depthMetric.DefinitionDomain
let depthValue = depthMetric[m]
orderby depthValue ascending
select new { m, depthValue }




Querying the Code Quality and Code Metrics

NDepend computes more than 80 code metrics, listed here. These code metrics are presented by the interfaces IAssembly, INamespace, IType, IMethod and IField.
// <Name>Quick summary of methods to refactor</Name>
warnif count > 0 from m in JustMyCode.Methods where
                                    
// Code Metrics' definitions
  m.NbLinesOfCode > 30 ||           // http://www.ndepend.com/Metrics.aspx#NbLinesOfCode
  m.NbILInstructions > 200 ||       // http://www.ndepend.com/Metrics.aspx#NbILInstructions
  m.CyclomaticComplexity > 20 ||    // http://www.ndepend.com/Metrics.aspx#CC
  m.ILCyclomaticComplexity > 50 ||  // http://www.ndepend.com/Metrics.aspx#ILCC
  m.ILNestingDepth > 5 ||           // http://www.ndepend.com/Metrics.aspx#ILNestingDepth
  m.NbParameters > 5 ||             // http://www.ndepend.com/Metrics.aspx#NbParameters
  m.NbVariables > 8 ||              // http://www.ndepend.com/Metrics.aspx#NbVariables
  m.NbOverloads > 6                 // http://www.ndepend.com/Metrics.aspx#NbOverloads

select new { m, m.NbLinesOfCode, m.NbILInstructions, m.CyclomaticComplexity, 
             
m.ILCyclomaticComplexity, m.ILNestingDepth, 
             
m.NbParameters, m.NbVariables, m.NbOverloads } 
Notes that many of these code metrics returns a nullable numeric value because they are not necessarily defined for all code elements. For example the #Lines of Code is not computed for third-party code elements.

Some of these code metrics are computed from the IL code contained in the application assemblies, some others are computed from the assembly PDB files (if found, else these metrics values are null) some others are computed from the source code itself (if found, else these metrics values are null). The document Understanding NDepend Analysis Inputs explains with details how code metrics are processed, from which sources.

Code Coverage Metrics
NDepend offers the possibility to import code coverage by tests data , from the result of the most popular .NET code coverage tool.

Amongst all code metrics, code coverage is certainly the one that tells best if a piece of code is bug prone or not. In this condition, it can be very informative to couple code coverage metrics, with facts like high complexity or code refactored. We know that complex and refactored code are typically bug prone, so we need to cover such code with tests to keep the bug probability low.
from m in Application.Methods
let percentageCoverage = m.PercentageCoverage
let CC = m.CyclomaticComplexity
let refactored = m.CodeWasChanged()

      
// match not full covered methods...
where percentageCoverage != null && percentageCoverage < 100 &&
      
// .. that are complex or that have been refactored
      (CC > 20 || refactored)

orderby CC descending
select new { m, CC, percentageCoverage, refactored }
Note that complex methods code should be refactored to several simple methods.
Note also that metrics like #Lines of Code and % coverage are presented by the interface ICodeContainer. Only the interface IField doesn't implement ICodeContainer.

Custom Metrics
Thanks to the LINQ flexibility it is easy to compose the default code metrics to create more elaborated code metrics, like for example:
// <Name>C.R.A.P method code metric</Name>
// Change Risk Analyzer and Predictor (i.e. CRAP) code metric
// This code metric helps in pinpointing overly complex and untested code.
// Reference: http://www.artima.com/weblogs/viewpost.jsp?thread=215899
// Formula:   CRAP(m) = comp(m)^2 * (1 – cov(m)/100)^3 + comp(m)
warnif count > 0
from m in JustMyCode.Methods

// Don't match too short methods
where m.NbLinesOfCode > 10

let CC = m.CyclomaticComplexity
let uncov = (100 - m.PercentageCoverage) / 100f
let CRAP = (CC * CC * uncov * uncov * uncov) + CC
where CRAP != null && CRAP > 30
orderby CRAP descending, m.NbLinesOfCode descending
select new { m, CRAP, CC, uncoveredPercentage = uncov*100, m.NbLinesOfCode }

We saw above in the section Querying the Code Dependencies and Design that a ICodeMetric<TCodeElement,TNumeric> object can be obtained to get a code metric equals to the depth of usage of one or several code elements.
A custom code metric object can also be obtained from the extension method ExtensionMethodsHelpers.FillIterative(). For example, this possibility is used in the rule to obtain dead types, but also to obtained types only used by dead type (and the depth of usage):
// <Name>Potentially dead Types</Name>
warnif count > 0
// Filter procedure for types that should'nt be considered as dead
let canTypeBeConsideredAsDeadProc = new Func<IType, bool>(
   
t => !t.IsPublic && //   Public types might be used by client applications of your assemblies.
         t.Name != "Program" && 
        
!t.IsGeneratedByCompiler &&
        
!t.HasAttribute("NDepend.Attributes.IsNotDeadCodeAttribute".AllowNoMatch()))
         
// If you don't want to link NDepend.API.dll
         // you can use your own IsNotDeadCodeAttribute and adapt this rule.

// Select types unused
let typesUnused = 
   
from t in JustMyCode.Types where
   
t.NbTypesUsingMe == 0 && canTypeBeConsideredAsDeadProc(t)
   
select t

// Dead types = types used only by unused types (recursive)
let deadTypesMetric = typesUnused.FillIterative(
types => from t in codeBase.Application.Types.UsedByAny(types).Except(types)
         
where canTypeBeConsideredAsDeadProc(t) &&
               
t.TypesUsingMe.Intersect(types).Count() == t.NbTypesUsingMe
         
select t)

from t in deadTypesMetric.DefinitionDomain
select new { t, t.TypesUsingMe, depth = deadTypesMetric[t] }




Querying the Code Diff

NDepend comes with the unique feature to compare two different snapshots of a code base to see what was changed/added/removed. In the NDepend API this feature is presented through the interface ICompareContext. For example, the following query enumerates methods where code has been changed:
from m in Application.Methods 
where context.CompareContext.CodeWasChanged(m)
select m
Actually, thanks to the extension methods in ExtensionMethodsCQLinqCompare you can just write the shortest query below, and the CQLinq compiler will take care to transform it into the query above:
from m in Application.Methods 
where m.CodeWasChanged()
select m
Once such query is written, the NDepend UI offers the two capabilities:
  • to compare the two source files versions of the method changed
  • to compare two decompiled (with Reflector) versions of the method body. This feature is very useful if you are analyzing some third-party assemblies without the source code.


The interfaces ICompareContext methods, and the extension methods in ExtensionMethodsCQLinqCompare takes a code element in argument, and returns a boolean indicating if the code element has been changed/added/removed. Notice the two methods OlderVersion() and NewerVersion() . As their names suggest, these methods returns the older or newer version of a code element, or null if the code element has been added (hence no older version) or removed (hence no newer version). These methods can be useful for example to write the query below that tracks the evolution in terms of method complexity:
// <Name>Methods that became more complex</Name>
from m in codeBase.OlderVersion().Methods 
where m.IsPresentInBothBuilds() 
let oldCC = m.CyclomaticComplexity
let newCC = m.NewerVersion().CyclomaticComplexity
where oldCC != null && newCC > oldCC
select new { m, oldCC, newCC }
Notice the call to IsPresentInBothBuilds to ensure that we only deal with methods that are both in the older and newer code base snapshot, to prevent any NullReferenceException while running the query!

As this last query shows, mixing the diff feature with others CQLinq features like code quality metrics or dependencies, can lead to powerful code queries and rules to track the evolution of a code base.




Querying the Naming of Code Elements

CQLinq proposes several facilities to query the name of the code elements. This is especially useful to write simple code naming conventions (based on regular expressions)...
// <Name>Abstract base class should be suffixed with 'Base'</Name>
warnif count > 0 from t in Application.Types where 
  
t.IsAbstract && 
  
t.IsClass &&

  
// equivalent to:   DepthOfDeriveFrom "System.Object" == 1
  t.DepthOfInheritance == 1 && 

  
((!t.IsGeneric && !t.NameLike (@"Base$")) ||
   
( t.IsGeneric && !t.NameLike (@"Base<")))
select new { t, t.DepthOfInheritance }
...or smart code naming conventions:
// <Name>Avoid naming types and namespaces with the same identifier</Name>

// Not only this can provoke compiler resolution collision,
// but also, this makes code less maintainable because
// concepts are not concisely identified.

warnif count > 0
let hashsetShortNames = Namespaces.Where(n => n.Name.Length > 0).Select(n => n.SimpleName).ToHashSet()

from t in JustMyCode.Types
where hashsetShortNames.Contains(t.Name)
select new { t, namespaces = Namespaces.Where(n => n.SimpleName == t.Name) }
The code elements naming feature is summarized in the CQLinq syntax document, in the section Matching code elements by name string.




Querying the States Mutability

The concept of immutability is becoming more and more popular amongst C# and VB.NET programmers. (rumors say that post v5 versions of C# and VB.NET will proposes some keywords concerning immutability). Immutability is especially useful when dealing with concurrent accesses into multi-threaded environment.

A type is considered as immutable if its instance fields cannot be modified once an instance has been built by a constructor. A static field is considered as immutable if it is private and if it is only assigned by the static constructor. An instance field is considered as immutable if it is private and if it is only assigned by its type’s constructor(s) or its type’s static constructor. Notes that a field declared as readonly is necessarily immutable, but a field can be immutable without being declared as readonly. In this last case, the keyword readonly can be added to the field declaration, without provoking any compilation error.

At analysis time, NDepend computes the mutability of types and fields. The result is available through the properties IType.IsImmutable and IField.IsImmutable. It is then easy to write such rule for example:
// <Name>Structures should be immutable</Name>
warnif count > 0 from t in Application.Types where 
   
t.IsStructure && 
  
!t.IsImmutable
let mutableFields = t.Fields.Where(f => !f.IsImmutable)
select new { t, t.NbLinesOfCode, mutableFields }

Since neither C# nor VB.NET proposes yet any keyword to enforce type immutability, it is possible to use an attribute like ImmutableAttribute (or any other custom attribute) coupled with a rule like the one below, to enforce immutability.
// <Name>Types immutable should be tagged with ImmutableAttribute</Name>
from t in Application.Types where 
  
!t.HasAttribute ("NDepend.Attributes.ImmutableAttribute".AllowNoMatch()) && 
  
t.IsImmutable
select new { t, t.NbLinesOfCode }

The two properties IMethod.ChangesObjectState and IMethod.ChangesTypeState can be use to enforce or check that a method is pure. A pure method is a method that doesn't assign any instance or static fields.

Also, to control the write access to a particular field, you can use the extension method ExtensionMethodsCQLinqDependency.AssignField():
from m in Methods where m.AssignField("NUnit.Core.TestResult.resultState")
select new { m, m.NbLinesOfCode }
In addition, the interface IField presents the 3 properties IField.MethodsAssigningMe , IField.MethodsReadingMeButNotAssigningMe and IField.MethodsUsingMe and the interface IMethod presents the method IMethod.AssignField().




Querying Source Files Paths

The interface ICodeElement presents the two properties ICodeElement.SourceFileDeclAvailable and ICodeElement.SourceDecls.
For a code element, its source file declaration(s) might not be available for a variety of reasons:
  • Because the source files or assemblies PDB files were not available at analysis time, as explained in details in the document Understanding NDepend Analysis Inputs.
  • Because the code coverage files were not available at analysis time (for code coverage related metrics).
  • Because NDepend doesn't gather source file declarations of third-party code elements.
  • Because it is a default constructor not declared in source code.
  • Because it is an abstract method or a field (for which NDepend doesn't gather yet source file declarations).
Having access to source file declarations opens a range of interesting applications. For example the default query matching methods to discard from the JustMyCode code base view, relies on some patterns on source file name, and can be easily adapted to any situation:
// <Name>Discard generated and designer Methods from JustMyCode</Name>
// --- Make sure to make this query richer to discard generated methods from NDepend rules results ---
notmycode 

//
// First define source files paths to discard
//
from a in Application.Assemblies 
where a.SourceFileDeclAvailable 
let asmSourceFilesPaths = a.SourceDecls.Select(s => s.SourceFile.FilePath)

let sourceFilesPathsToDiscard = (
    
from filePath in asmSourceFilesPaths 
    
let filePathLower= filePath.ToString().ToLower()
    
where     
      
filePathLower.EndsWithAny(
        
".g.cs",        // Popular pattern to name generated files.
        ".g.vb",
        
".xaml",        // notmycode WPF xaml code
        ".designer.cs", // notmycode C# Windows Forms designer code
        ".designer.vb") // notmycode VB.NET Windows Forms designer code
       ||
       
// notmycode methods in source files in a directory containing generated
       filePathLower.Contains("generated")
  
select filePath
).ToHashSet() 
  
//
// Second: discard methods in sourceFilesPathsToDiscard 
//
from m in a.ChildMethods
where (m.SourceFileDeclAvailable && 
       
sourceFilesPathsToDiscard.Contains(m.SourceDecls.First().SourceFile.FilePath)) ||
      
// Generated methods might be tagged with this attribute
      m.HasAttribute ("System.CodeDom.Compiler.GeneratedCodeAttribute".AllowNoMatch())
select new { m, m.NbLinesOfCode }
Notice that source files paths are represented through the API NDepend.Path designed to make paths operations convenient (absolute/relative path, directory/file path, navigation...).

Several default rules concerning source files organization are proposed, like the following one. Notice that this rule relies on the property IAssembly.VisualStudioProjectFilePath . The Visual Studio project file path is found by NDepend at analysis time through an heuristic.
// <Name>Avoid referencing source file out of Visual Studio project directory</Name>

// A source file located outside of the VS project directory can be add through:
//  > Add > Existing Items... > Add As Link
//
// Don't use this possibility to share code accross several assemblies.
// This provoques type duplication at binary level.
// Hence maintainability is degraded and subtle versioning bug can appear.
// Prefer sharing types through classic libraries.
//
// This practice can be tolerated for certain types shared accross executable assemblies.
// Such type can be responsible for particular and not shareable startup related concerns, 
// such as registering custom assembly resolving handlers or 
// checking the .NET Framework version before loading any custom library.
warnif count > 0 

from a in Application.Assemblies
where a.VisualStudioProjectFilePath != null
let vsProjDirPathLower = a.VisualStudioProjectFilePath.ParentDirectoryPath.ToString().ToLower()

from t in a.ChildTypes
where JustMyCode.Contains(t) && t.SourceFileDeclAvailable

from decl in t.SourceDecls
let sourceFilePathLower = decl.SourceFile.FilePath.ToString().ToLower()
where sourceFilePathLower .IndexOf(vsProjDirPathLower) != 0
select new { t, sourceFilePathLower , projectFilePath = a.VisualStudioProjectFilePath.ToString() }