I am looking for an elegant way of statically referencing a property attribute in C#. To give you an example, say I have this class:
public class A
{
[Attribute(Name="myAttributeName")]
public string Property1 { get; set; }
}
Now, I see the attribute as quite similar to a static member of a class, so in my mind, there should be an easy way to access the attribute from outside the class; e.g. through a similar operator to typeof or nameof (but it would return a list of attributes, since there may be multiple attributes to fetch). The way I would like to use this operator is as follows:
public class B
{
// Through an attribute definition
[Attribute2(attrof(A.Property1))]
public string Property2 { get; set; }
// In a method
public void method()
{
var attrs = attrof(A.property1);
}
}
I think I have found one way to make it work with two parameters like the example below - at least for the method invocation. Passing variables to attributes doesn't seem to work in C#, but that's nevertheless the way I'd like to construct my code.
public class C
{
public static object[] GetAttrs(Type type, string propertyName)
{
return type.GetProperty(propertyName).GetCustomAttributes(true);
}
}
public class A
{
[Attribute1(Name="myAttributeName")]
public string Property1 { get; set; }
}
public class B
{
// Through an attribute definition
// Unfortunately, passing variable to attrs not supported
// so this does not work
[Attribute2(C.GetAttrs(typeof(A), nameof(A.Property1)))]
public string Property2 { get; set; }
// In a method
public void method()
{
var attrs = C.GetAttrs(typeof(A), nameof(A.Property1));
}
}
However, it feels tedious to pass references to both the class and property, when syntactically, A.Property1 contains information about both - something a compiler should be able to draw information from. Therefore, I wonder if any such operator exists today, or if there are any other ideas on how this functionality could be achieved?
EDIT: I just thought about the B.Property2 attribute definition one more time and thought that it should still be possible to get this working, since I think attributes are constant. Or am I missing something here?
There is no default operator for such case, but you could implement something similar. Code to extract value from A.Property1 attribute is in Main function
using System;
using System.Reflection;
namespace ConsoleApp16
{
public class CustomAttribute : Attribute
{
public string Name { get; }
public CustomAttribute(string name)
{
Name = name;
}
}
public class ReferenceAttribute : Attribute
{
public string PropertyName { get; }
public Type Type { get; }
public ReferenceAttribute(Type type, string propertyName)
{
Type = type;
PropertyName = propertyName;
}
}
public class A
{
[Custom("text")]
public string Property1 { get; set; }
}
public class B
{
[Reference(typeof(A), nameof(A.Property1))]
public string Property { get; set; }
}
class Program
{
static void Main(string[] args)
{
var referenceAttribute = typeof(B).GetProperty(nameof(B.Property))
.GetCustomAttribute<ReferenceAttribute>();
var customAttribute = referenceAttribute.Type.GetProperty(referenceAttribute.PropertyName)
.GetCustomAttribute<CustomAttribute>();
Console.WriteLine(customAttribute.Name);
}
}
}
Related
I have the following structure:
public class LogicStatement : ILogicStatement
{
public string TestLogic { get; set; }
public string CompareLogic { get; set; }
public string Operator { get; set; }
public string Expression();
public bool Value();
}
public class Test : ITest
{
public int TestId { get; set; }
public int LiteralId { get; set; }
public string TestName { get; set; }
public string TestText { get; set; }
public string TestDisplayName { get; }
**public ILogicStatement LogicStatement { get; set; }**
public string Expression { get; set; }
public bool Value { get; set; }
}
public class Literal : ILiteral
{
some property members...
**public List<ITest> Tests {get; set;}**
some method members...
}
Note that the class Test has a member of type LogicStatement, and the class Literal has a member of type List.
Note also that all classes have properties and methods that share the same name: Expression, Value, Expression(), Value().
The value of Expression and Value (properties and methods) depend on values in the LogicStatement class.
Throughout the whole project, I use the Interface Type for to instantiate each object to adhere with Dependency Inversion. To support this, I use a factory-like design to create new instances of Test and LogicStatement.
Example:
public static class Factory
{
public static ILogicStatement CreateLogicStatement()
{
return new LogicStatement();
}
public static ITest CreateTest()
{
return new Test(CreateLogicStatement());
}
public static List<ITest> CreateTests()
{
return new List<ITest>();
}
//repeat the same for evey other class.
}
My goal is to have Expression() and Value() be calculated only once in the bottom level class (LogicStatement), and somehow get transfered to their counterpart properties in the higher level classes.
I'm getting the data from Dapper and it looks like all the nested objects are returned from the Dapper module correctly with the same nested structure I intended, and with the right values for all of their members. All of them but Expression, Expression(), Value, Value() are null.
my constructors look like this:
public LogicStatement()
{
Expression();
Value();
}
public Test(ILogicStatement logicStatement)
{
_logicStatement = logicStatement;
Expression = _logicStatement.Expression();
Value = _logicStatement.Value();
}
public Literal(ITest test)
{
_test = test;
Expression = _test.Expression;
Value = _test.Value;
}
and my main:
List<ILiteral> literals = Factory.CreateLiterals();
List<ITest> tests = Facotry.CreateTests();
List<ILogicStatement> logicStatements = Factory.CreateLogicStatements();
literals = GetDataFromDapper();
This last line seems to assign correct values to all other members on all hierarchies. But I cannot get Expression and Value to be anything other than null.
If I test LogicStatement.Expression() and LogicStatement.Value() standalone, they do return the expexted values. but starting at the first parent class Test, these properties are all null.
I think I'm doing something wrong in the way i'm instantiating my objects. Primarily because I'm not sure i understand basic best practices to write constructors.
Maybe I the desired behavior should be implemented through events, where the Test and Literal classes subscribe to changes in the Expression() and Value() methods (or rather to what calculates them). But I never used events and I'd like to know if this fundamentally can be acheived without them first.
My question: How do I make the Expression() Value() at the bottom level class "Fire up" whenever LogicStatement is instantiated, and then have the Expression and Value properties be assigned accordingly as a result.
In other words, I want the following to always be true:
test[i].Expression == literal[i].Expression == LogicStatement[i].Expression()
I'm a beginner in OOP. So any fundamental explanation is welcome.
As you are new to object oriented programming I would start with the basics and leave factories and adhering with Dependency Inversion and the interfaces away for later.
You could tell Dapper to split joined tables into multiple entities (see https://www.learndapper.com/relationships), but for learning OOP I would start doing everything manually.
Your class design does not look proper to me yet. Not sure what Expression and Value of the LogicStatement are, but if they are calculations based on the other properties, I would implement them as (just to show off with complicated words) lazy initialized cached getter properties that are invalidated in the setters of the relevant properties. That ensures you only calculate them once for as many reads you like but recalculate them on first read after one or multiple properties have been updated.
public class LogicStatement {
private string _testLogic;
private string _compareLogic;
private string _operator;
private string? _expression;
private bool? _value;
public LogicStatement(string testLogic, string compareLogic, string #operator) {
_testLogic = testLogic;
_compareLogic = compareLogic;
_operator = #operator;
}
public string TestLogic {
get {
return _testLogic;
}
set {
_testLogic = value;
InvalidateCachedValues();
}
}
public string CompareLogic {
get {
return _compareLogic;
}
set {
_compareLogic = value;
InvalidateCachedValues();
}
}
public string Operator {
get {
return _operator;
}
set {
_operator = value;
InvalidateCachedValues();
}
}
public string Expression {
get {
string? result = _expression;
if (result is null) {
_expression = result = BuildExpression();
}
return result;
}
}
public bool Value {
get {
bool? result = _value;
if (result is null) {
_value = result = EvaluateValue();
}
return result.Value;
}
}
private void InvalidateCachedValues() {
_expression = null;
_value = null;
}
private string BuildExpression() {
//Your logic goes here
throw new NotImplementedException();
}
private bool EvaluateValue() {
//Your logic goes here
throw new NotImplementedException();
}
}
Sorry, it got a bit bigger with the full properties.
In the other classes I would not copy the Value and the Expression but simply remove these properties as anybody can easily access them through the LogicStatement property:
public class Test {
public Test(int testId, int literalId, string testName, string testText, string testDisplayName, LogicStatement logicStatement) {
TestId = testId;
LiteralId = literalId;
TestText = testText;
TestDisplayName = testDisplayName;
LogicStatement = logicStatement;
}
public int TestId { get; }
public int LiteralId { get; }
public string TestName { get; }
public string TestText { get; }
public string TestDisplayName { get; }
public LogicStatement LogicStatement { get; }
}
and the Literal could look like this (I got a bit confused whether this class has one Test or a list of them, I stick to your constructor + properties that hint in the direction of a single one):
public class Literal {
private Test _test;
public Literal(string property1, int property2, Test test) {
Property1 = property1;
Property2 = property2;
_test = test;
}
public string Property1 { get; }
public int Property2 { get; }
public string Expression => _test.LogicStatement.Expression;
public bool Value => _test.LogicStatement.Value;
}
As you decided not to expose the Test in the Literal it makes sense to provide Expression and Value, otherwise they could also be removed (or kept for convenience).
I need to have something like this. So a class that implements this Interface needs to get a property with the same type as the class.
Is this even possible, ifso how? I'm using .net 6.
public interface IProperty
{
public typeof(this) parameter { get; } // doesn't work, can't use typeof()
}
public class clsResourceProperty : IProperty
{
public clsResourceProperty parameter { get; }
}
public class clsInterfaceProperty : IProperty
{
public clsInterfaceProperty parameter { get; }
}
I know how to use generic interfaces, and with the second example it works, but clsResourcePropertyGeneric: IPropertyGeneric looks strange. And doens't work for the application i need.
public interface IPropertyGeneric<T>
{
public T parameter { get; }
}
public class clsResourcePropertyGeneric: IPropertyGeneric<clsResourcePropertyGeneric>
{
public clsResourcePropertyGeneric parameter { get; }
}
public class clsInterfacePropertyGeneric: IPropertyGeneric<clsInterfacePropertyGeneric>
{
public clsInterfacePropertyGeneric parameter { get; }
}
In the application i need, i need to have a class containing a list of this interface. So something like this:
public class clsState
{
public List<IProperty> data {get; private set;}
public clsState(List<IProperty> data)
{
this.data = data;
}
public void logic()
{
foreach(var d in data)
{
//do something with d.parameters
}
}
}
But this doesn't work with the generic interface. I need to make a class containing a list of this interface, where i define the generic type T. But this list can't contain ALL classes which implement this interface
public class clsState<T>
// need to add T here to use it in the list, but the list needs to contain ALL implementing class types, not only 1
{
public List<IProperty<T>> data {get; private set;}
public clsState(List<IProperty<T>> data)
{
this.data = data;
}
public void logic()
{
foreach(var d in data)
{
//do something with d.parameters
}
}
}
I found this link, but this is from 7 years ago, so maybe there is some evolution in this aspect?
You can use the interface as your property type, as in:
public interface IProperty
{
public IProperty parameter { get; }
}
public class clsResourceProperty : IProperty
{
public IProperty parameter { get; }
}
public class clsInterfaceProperty : IProperty
{
public IProperty parameter { get; }
}
As for having a collection of the interfaces, it is possible to collect all of the classes for a particular type or interface. This is from a piece of code in one of my libraries. It doesn't do exactly what you're after, but it might be a step towards your final solution.
private static Type[] strategyTypes;
private readonly static Type[] obsoleteTypes = new Type[]
{
};
static StrategyRepository()
{
strategyTypes = Assembly.GetExecutingAssembly().GetTypes()
.Where(t => t.BaseType == typeof(Strategy))
.Except(obsoleteTypes)
.ToArray();
}
This question might be a more direct answer to that part of your question: Getting all types that implement an interface
I have a series of classes used to represent identifiers in my project that are supposed to have a specific string storage format. I don't have control on this format.
The classes are pure containers, they don't do anything. The storage format is of the form "CLASSSTYPE|key1|key2|key3|...|keyN". Each "key" can be mapped to one property of the class.
Right now the FromStorageString and ToStorageString functions look like this:
public class SomeTypeId : IObjectId
{
public static string ToStorageString(SomeTypeId id)
{
return string.Format("{0}|{1}|{2}", typeof(SomeTypeId).Name, MyIntKey, MyStringKey);
}
public static SomeTypeId FromStorageString(IdReader source)
{
int intKey = source.Retrieve<int>();
string stringKey = source.Retrieve<string>();
return new SomeTypeId(intKey, stringKey);
}
public int MyIntKey { get; private set; }
public string MyStringKey { get; private set; }
public SomeTypeId(int intKey, string stringKey)
{
MyIntKey = intKey;
MyStringKey = stringKey;
}
}
We are checking the From/To consistency in unit tests, but I feel there should be a way to simplify the set up and perform the check a compile-time.
What I had in mind is something like this:
[Storage("MyIntKey", "MyStringKey")]
public class SomeTypeId : IObjectId
{
private SomeTypeId() {}
public int MyIntKey { get; private set; }
public string MyStringKey { get; private set; }
public SomeTypeId(int intKey, string stringKey)
{
MyIntKey = intKey;
MyStringKey = stringKey;
}
}
But first I don't know how to do this with the no parameters constructor and the property setters staying private. I am reluctant to have them public.
Second this approach is not robust to property name change and typos because the property names in the attribute are strings.
Should I expose the setters and private constructor ?
Is there a better way of doing this ?
I'm working on a project where the API methods I write have to return different "views" of domain objects, like this:
namespace View.Product
{
public class SearchResult : View
{
public string Name { get; set; }
public decimal Price { get; set; }
}
public class Profile : View
{
public string Name { get; set; }
public decimal Price { get; set; }
[UseValidationRuleset("FreeText")]
public string Description { get; set; }
[SuppressValidation]
public string Comment { get; set; }
}
}
These are also the arguments of setter methods in the API which have to be validated before storing them in the DB. I wrote an object validator that lets the user define validation rulesets in an XML file and checks if an object conforms to those rules:
[Validatable]
public class View
{
[SuppressValidation]
public ValidationError[] ValidationErrors
{
get { return Validator.Validate(this); }
}
}
public static class Validator
{
private static Dictionary<string, Ruleset> Rulesets;
static Validator()
{
// read rulesets from xml
}
public static ValidationError[] Validate(object obj)
{
// check if obj is decorated with ValidatableAttribute
// if not, return an empty array (successful validation)
// iterate over the properties of obj
// - if the property is decorated with SuppressValidationAttribute,
// continue
// - if it is decorated with UseValidationRulesetAttribute,
// use the ruleset specified to call
// Validate(object value, string rulesetName, string FieldName)
// - otherwise, get the name of the property using reflection and
// use that as the ruleset name
}
private static List<ValidationError> Validate(object obj, string fieldName, string rulesetName)
{
// check if the ruleset exists, if not, throw exception
// call the ruleset's Validate method and return the results
}
}
public class Ruleset
{
public Type Type { get; set; }
public Rule[] Rules { get; set; }
public List<ValidationError> Validate(object property, string propertyName)
{
// check if property is of type Type
// if not, throw exception
// iterate over the Rules and call their Validate methods
// return a list of their return values
}
}
public abstract class Rule
{
public Type Type { get; protected set; }
public abstract ValidationError Validate(object value, string propertyName);
}
public class StringRegexRule : Rule
{
public string Regex { get; set; }
public StringRegexRule()
{
Type = typeof(string);
}
public override ValidationError Validate(object value, string propertyName)
{
// see if Regex matches value and return
// null or a ValidationError
}
}
Phew... Thanks for reading all of this. I've already implemented it and it works nicely, and I'm planning to extend it to validate the contents of IEnumerable fields and other fields that are Validatable.
What I'm particularly concerned about is that if no ruleset is specified, the validator tries to use the name of the property as the ruleset name. (If you don't want that behavior, you can use [SuppressValidation].) This makes the code much less cluttered (no need to use [UseValidationRuleset("something")] on every single property) but it somehow doesn't feel right. I can't decide if it's awful or awesome. What do you think?
Any suggestions on the other parts of this design are welcome too. I'm not very experienced and I'm grateful for any help.
Also, is "Validatable" a good name? To me, it sounds pretty weird but I'm not a native English speaker.
My suggestion uses an interface instead attributes:
public interface IValidatable
{
ValidationError[] Validate(Rulesets ruleSets);
}
public class View : IValidatable
{
public ValidationError[] Validate(Rulesets ruleSets)
{
// do validate
}
}
public static class Validator
{
private static Rulesets _rulesets;
static Validator()
{
// read rulesets
}
public static ValidationError[] Validate(object obj)
{
IValidatable validObj = obj as IValidatable;
if (obj == null)
// not validatable
return new ValidationError[0];
return validObj.Validate(_rulesets);
}
}
Give a class like below, how can i find the name of one particluar property?
public class Student
{
public int Grade
{
get;
set;
}
public string TheNameOfTheGradeProperty
{
get
{
return ????
}
}
// More properties..
}
So i would like to return the string "Grade" from the TheNameOfTheGradeProperty property. The reason i'm asking is that i do not want to use a hardcoded string, but rather a lambda expression or something else.
How can i acheive this?
It is possible to use an expression to find the name of the property, using a simple extension method you can use it on any object... if you need to restrict it to a set of objects you can apply a generic constraint on T. Hope this helps
public class Student
{
public int Grade { get; set;}
public string Name { get; set; }
public string GradePropertyName
{
get { return this.PropertyName(s => s.Grade); }
}
public string NamePropertyName
{
get { return this.PropertyName(s => s.Name); }
}
}
public static class Helper
{
public static string PropertyName<T, TProperty>(this T instance, Expression<Func<T, TProperty>> expression)
{
var property = expression.Body as MemberExpression;
if (property != null)
{
var info = property.Member as PropertyInfo;
if (info != null)
{
return info.Name;
}
}
throw new ArgumentException("Expression is not a property");
}
}
You have a very strange request. Are you saying you want to not use a hard-coded string because you want TheNameOfTheGradeProperty to stay up to date if you refactor the class? If so, here's a strange way to do so:
public class Student
{
public int Grade { get; set; }
public string TheNameOfTheGradeProperty
{
get
{
Expression<Func<int>> gradeExpr = () => this.Grade;
MemberExpression body = gradeExpr.Body as MemberExpression;
return body.Member.Name;
}
}
}
using System.Reflection;
return typeof(Student).GetProperty("Grade").Name;
But as you can see, you're not that far ahead using reflection (in this manner) because the "Grade" string is still hard-coded which means in this scenario it's more efficient just to return "Grade".
One thing I like to do is create and add a custom attribute to a member like so. The following prevents you from having to use the hard-coded string "Grade".
public class Student {
// TAG MEMBER WITH CUSTOM ATTRIBUTE
[GradeAttribute()]
public int Grade
{
get;
set;
}
public string TheNameOfTheGradeProperty
{
get
{
/* Use Reflection.
Loop over properties of this class and return the
name of the one that is tagged with the
custom attribute of type GradeAttribute.
*/
}
}
// More properties..
}
Creating custom attributes can be found here.