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# McRule
Rule based filtering using expression trees.
## Predicate Grammar
Predicates are built using simple syntax to select comparison operators and methods for the specified properties on a supplied object of a specified type.
That is the policy specifies the type by name, property to match against and the value the property must have.
A simple equality comparison is used by default but operators can be prefixed to a policy operand for customized behavior, as shown below.
| Property Type | Operator | Comparison Description |
| string | * | Astrisk can appear at the beginning, end or both denoting: StartsWith, EndsWith or Contains respectively. |
| string | ~ | Denotes case-insensitive comparison when used in .net, things that translate the resulting expression tree may not respect this. EF core for instance won't bind a Contains with case insensitive comparison from the string methods at all, results in a runtime error. Note: when used with wildcard, tilde operator must be first: '~*foo'. |
| string | ! | Negative expression. Must prefix all other operators. |
| IComparable | > | Greater-than comparison. |
| IComparable | >= | Greater-than or equal to comparison. |
| IComparable | < | Less-than comparison. |
| IComparable | <= | Less-than or equal to comparison. |
| IComparable | <>, !=, ! | Not-equal to comparison. |
> Note: the IComparable interface is mostly used for numerical types but custom types with comparison providers may work at runtime.
> Note: initial IDictionary support has been added but only for collections where the value types are strings. When missing keys are encountered, evaluation defaults to false.
### Literal Values
Literal values, as needed, use handlbar syntax: {{ value }}. Null checks are implicitly added to most expressions but sometimes you need an expression that evaluates true for null values. In that case, a null literal is represented as {{null}}.
Case sensitivity doesn't matter, nor does internal whitespace inside the braces. Values are interpretted like so:
var matched = handlebarPattern.Match(value);
if (matched.Success) {
switch (matched.Groups.FirstOrDefault(x => x.Name == "literal")?.Value?.Trim()?.ToLower()) {
case "null":
return (true, new NullValue());
### Examples
## Notes
Publish nuget package:
cd McRule/bin/Release
dotnet publish -c release ../../
dotnet nuget push McRule.0.0.5.nupkg --api-key <api key> --source