[英]Using expressions to define validation rules
我想創建一個通用的驗證類,因此可以執行以下操作:
Validation v = new Validation();
v.AddRequired(x => this.Name);
v.AddRange(x => x.this.Age, 5, 65);
我不確定如何編寫方法定義並進行評估?
其中AddRequired
將采用string
而AddRange
將采用數值類型( int
,主要也是double
, decimal
等)
應該有一些可用於此任務的庫。 但是,您可以自己編寫,以獲取有關lambda的一些經驗。 我已經為AddRange
了一個實現草案,希望您可以從這里走得更遠。
public class Validation<T> {
private List<RangeValidation> _rangeValidations = new List<RangeValidation>();
public void AddRange(Func<T, int> func, int min, int max) {
_rangeValidations.Add(new RangeValidation() {
func = func,
min = min,
max = max
});
}
public bool Validate(T obj) {
foreach (var rangeValidation in _rangeValidations) {
int value = rangeValidation.func(obj);
if (value < rangeValidation.min || value > rangeValidation.max)
return false;
}
return true;
}
private class RangeValidation {
public Func<T, int> func;
public int min, max;
}
}
使Validation
對x
的類型通用,根據需要定義采用Func<x,object>
或其他某種類型的方法,存儲這些函數,然后從Validate(x)
方法中調用它們:
class Validation<T> {
private IList<Tuple<Func<T,IComparable>,IComparable,IComparable>> rangeChecks = new List<Tuple<Func<T,IComparable>,IComparable,IComparable>>();
private IList<Func<T,object>> nullChecks = new List<Func<T,object>>;
public AddRequired(Func<T,object> f) {
nullChecks.Add(f);
}
public AddRange(Func<T,IComparable> f, IComparable low, IComparable high) {
rangeChecks.Add(Tuple.Create(f, low, high));
}
public bool Validate(T x) {
foreach(var t in rangeChecks) {
var f = t.Item1;
var low = t.Item2;
var high = t.Item3;
var val = f(x);
if (v.CompareTo(low) < 0 || v.CompareTo(high) > 0) {
return false;
}
}
foreach (var t in nullChecks) {
if (t(x) == null) {
return false;
}
}
return true;
}
}
此實現非常簡單-它需要在許多地方進行null檢查才有用。 另外,它不是很有效,因為IComparable
和object
可以包裝值類型。 但是,傳遞和存儲Func<T,...>
對象的方式應該使您了解如何實現其余的功能。
一種方法是:
class ObjectToBeValidated {
public string Name { get; set; }
public int Age { get; set; }
}
class Validation {
private List<Expression<Func<ObjectToBeValidated, bool>>> requiredExpressions;
private List<Expression<Func<ObjectToBeValidated, bool>>> rangeExpressions;
public void AddRequired(Expression<Func<ObjectToBeValidated, string>> expression)
{
Expression<Func<ObjectToBeValidated, bool>> checkRequired = (p => !string.IsNullOrEmpty(expression.Compile().Invoke(p)));
requiredExpressions.Add(checkRequired);
}
public void AddRange(Expression<Func<ObjectToBeValidated, int>> expression, int min, int max)
{
Func<ObjectToBeValidated, int> compiledFunc = expression.Compile();
Expression<Func<ObjectToBeValidated, bool>> checkRange = (p => compiledFunc.Invoke(p) >= min && compiledFunc.Invoke(p) < max);
rangeExpressions.Add(checkRange);
}
}
這只會將您的條件存儲在List<T>
。 然后,您必須在Validation
類中添加一個方法來評估表達式:
public bool IsValid(ObjectToBeValidated testObject)
{
return requiredExpressions.All(p => p.Compile().Invoke(testObject))
&& rangeExpressions.All(p => p.Compile().Invoke(testObject));
}
然后像這樣使用:
validator.AddRequired(p => p.Name);
validator.AddRange(p => p.Age, 6, 15);
var myObject = new ObjectToBeValidated();
var result = validator.IsValid(myObject);
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