/// <summary>
/// This function complies a RuleModel r and returns a complied function
/// This uses the BuildExpr function.
/// The functions use LINQ Lambda Expressions to read the strings in the RuleModels and build and expression function.
/// </summary>
/// <typeparam name="T">RuleModel type but not really restricted</typeparam>
/// <param name="r">the rulemodel to complie</param>
/// <returns>complied bool function that checks wat the user wanted</returns>
public static Func <T, bool> CompileRule <T>(RuleModel r)
{
if (r.Operation.Equals(RuleModel.everythingElseRuleString)) // if the function is everything else is the last tag than ,make a function that makes everything last tag
{
var exp = Expression.Lambda <Func <T, bool> >(Expression.Constant(true), Expression.Parameter(typeof(T), "_")); // basicly this function always returns true.
return(exp.Compile());
}
else
{
var paramUser = Expression.Parameter(typeof(T));
Expression expr = BuildExpr <T>(r, paramUser);
// build a lambda function User->bool and compile it
return(Expression.Lambda <Func <T, bool> >(expr, paramUser).Compile());
}
}
static Expression BuildExpr <T>(RuleModel r, ParameterExpression param)
{
var left = MemberExpression.Property(param, r.Parameter);
var tProp = typeof(T).GetProperty(r.Parameter).PropertyType;
ExpressionType tBinary;
// is the operator a known .NET operator?
if (ExpressionType.TryParse(r.Operation, out tBinary))
{
var right = Expression.Constant(Convert.ChangeType(r.Constant, tProp));
// use a binary operation, e.g. 'Equal' -> 'u.Age == 15'
return(Expression.MakeBinary(tBinary, left, right));
}
else
{
MethodInfo method = null;
var methods = tProp.GetMethods();
foreach (var m in methods)
{
if (m.Name.Equals(r.Operation))
{
if (m.Name.Equals("Contains"))
{
if (m.Equals(StringContainExpressionMethodInfo))
{
var tParam2 = m.GetParameters()[0].ParameterType;
var right2 = Expression.Constant(Convert.ChangeType(r.Constant, tParam2));
var ignoreCase = Expression.Constant(StringComparison.CurrentCultureIgnoreCase);
return(Expression.Call(left, m, new Expression[] { right2, ignoreCase }));
}
}
else if (m.GetParameters().Length == 1)
{
method = m;
break;
}
}
}
var tParam = method.GetParameters()[0].ParameterType;
var right = Expression.Constant(Convert.ChangeType(r.Constant, tParam));
// use a method call, e.g. 'Contains' -> 'u.Tags.Contains(some_tag)'
return(Expression.Call(left, method, right));
}
}
