DataFilters.Queries 0.12.0

Datafilters

A small library that allow to convert a string to a generic IFilter object. Highly inspired by the elastic query syntax, it offers a powerful way to build and query data with a syntax that's not bound to a peculiar datasource.

Disclaimer

This project adheres to Semantic Versioning.

Major version zero (0.y.z) is for initial development. Anything MAY change at any time.

The public API SHOULD NOT be considered stable.

Table of contents

• <a href='#parsing'>Parsing</a>
• <a href='#filtering'>Filters syntax</a>
  • <a href='#equals-expression'>Equals</a>
  • <a href='#starts-with-expression'>Starts with</a>
  • <a href='#ends-with-expression'>Ends with</a>
  • <a href='#contains-expression'>Contains</a>
  • <a href='#isempty-expression'>Is empty</a>
  • <a href='#any-of-expression'>Any of</a>
  • <a href='#isnull-expression'>Is null</a>
  • <a href='#interval-expressions'>Interval expressions</a>
    • <a href='#gte-expression'>Greater than or equal</a>
    • <a href='#lte-expression'>Less than or equal</a>
    • <a href='#btw-expression'>Between</a>
  • <a href='#regular-expression'>Regular expression</a>
  • <a href="logic-operators">Logical operators</a>
    • <a href='#and-expression'>And</a>
    • <a href='#or-expression'>Or</a>
    • <a href='#not-expression'>Not</a>
  • <a href='#special-character-handling'>Special character handling</a>
  • <a href='#sorting'>Sorting</a>
• <a href='#how-to-install'>How to install</a>
• <a href='#how-to-use'>How to use</a>
  • <a href='#how-to-use-client'>On the client</a>
  • <a href='#how-to-use-backend'>On the backend</a>

The idea came to me when working on a set of REST APIs and trying to build /search endpoints. I wanted to have a uniform way to query a collection of resources whilst abstracting away underlying datasources.

Let's say your API handles vigilante resources :

public class Vigilante
{
    public string Firstname { get; set; }
    public string Lastname { get; set; }
    public string Nickname {get; set; }
    public int Age { get; set; }
    public string Description {get; set;}
    public IEnumerable<string> Powers {get; set;}
    public IEnumerable<Vigilante> Acolytes {get; set;} 
}

JSON Schema

{
  "id": "vigilante_root",
  "title": "Vigilante",
  "type": "object",
  "properties": {
    "firstname": {
      "required": true,
      "type": "string"
    },
    "lastname": {
      "required": true,
      "type": "string"
    },
    "nickname": {
      "required": true,
      "type": "string"
    },
    "age": {
      "required": true,
      "type": "integer"
    },
    "description": {
      "required": true,
      "type": "string"
    },
    "powers": {
      "required": true,
      "type": "array",
      "items": {
        "type": "string"
      }
    },
    "acolytes": {
      "required": true,
      "type": "array",
      "items": {
        "$ref": "vigilante_root"
      }
    }
  }
}

and the base URL of your API is https://my-beautiful/api.

vigilante resources could then be located at https://my-beautiful/api/vigilantes/

Wouldn't it be nice to be able to search any resource like so https://my-beautiful/api/vigilantes/search?nickname=Bat*|Super* ?

This is exactly what this project is about : giving you an uniform syntax to query resources without having to think about the underlying datasource.

<a href='#' id='parsing'>Parsing</a>

This is the first step on filtering data. Thanks to SuperPower, the library supports a custom syntax that can be used to specified one or more criteria resources must fullfill. The currently supported syntax mimic the query string syntax : a key-value pair separated by ampersand (& character) where :

• field is the name of a property of the resource to filter
• value is an expression which syntax is highly inspired by the Lucene syntax

To parse an expression, simply call ToFilter<T> extension method (see unit tests for more details on the syntax)

<a href='#' id='filtering'>Filters syntax</a>

Several expressions are supported and here's how you can start using them in your search queries.

<a href='#' id='equals-expression'>Equals</a>

Search for any vigilante resource where nickname value is manbat

<a href='#' id='starts-with-expression'>Starts with</a>

Search for any vigilante resource that starts with "bat" in the nickname property

<a href='#' id='ends-with-expression'>Ends with</a>

Search for vigilante resource that ends with man in the nickname property.

<a href='#' id='contains-expression'>Contains</a>

Search for vigilante resources that contains bat in the nickname property.

💡 contains also work on arrays. powers=*strength* will search for vigilantes who have strength related powers.

<a href='#' id='isempty-expression'>Is empty</a>

Search for vigilante resources that have no powers.

<a href='#' id='isnull-expression'>Is null</a>

Search for vigilante resources that have no powers.

<a href='#' id='any-of-expression'>Any of</a>

Search for vigilante resources that have at least one of the specified powers.

will result in a IFilter instance equivalent to

IFilter filter = new MultiFilter
{
     Logic = Or,
     Filters = new IFilter[]
     {
         new Filter("powers", EqualTo, "strength"),
         new Filter("powers", EqualTo, "speed"),
         new Filter("powers", EqualTo, "size")
     }
};

<a href='#' id='isnull-expression'>Is null</a>

Search for vigilante resources that have no powers.

<a href='#' id='interval-expressions'>Interval expressions</a>

Interval expressions are delimited by upper and a lower bound. The generic syntax is

<field>=<min> TO <max>

where

• field is the name of the property current interval expression will be apply to
• min is the lowest bound of the interval
• max is the highest bound of the interval

<a href='#' id='gte-expression'>Greater than or equal</a>

Search for vigilante resources where the value of age property is greater than or equal to 18

<a href='#' id='lte-expression'>Less than or equal</a>

Search for vigilante resource where the value of age property is lower than 30

IFilter filter = new Filter("age", LessThanOrEqualTo, 30);

### <a href='#' id='btw-expression'>Between</a>

Search for vigilante resources where `age` property is between `20` and `35`

| Query string     | JSON                                                                                                          | C#                                                                                                                                                    |
| ---------------- | ------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------- |
| `age=[20 TO 35]` | `{"logic": "and", filters[{"field":"age", "op":"gte", "value":20}, {"field":"age", "op":"lte", "value":35}]}` | `new MultiFilter { Logic = And, Filters = new IFilter[] { new Filter ("age", GreaterThanOrEqualTo, 20), new Filter("age", LessThanOrEqualTo, 35) } }` |


---
💡 You can exclude the lower (resp. upper) bound by using `]` (resp. `[`). 
- `age=]20 TO 35[` means `age` strictly greater than `20` and strictly less than`35`
- `age=[20 TO 35[` means `age` greater than or equal to `20` and strictly less than`35`
- `age=]20 TO 35]` means `age` greater than `20` and less than or equal to `35`
  
💡 Dates, times and durations must be specified in [ISO 8601 format](https://en.wikipedia.org/wiki/ISO_8601)

Examples :
- `]1998-10-26 TO 2000-12-10[`
- `my/beautiful/api/search?date=]1998-10-26 10:00 TO 1998-10-26 10:00[`
- `]1998-10-12T12:20:00 TO 13:30[` is equivalent to `]1998-10-12T12:20:00 TO 1998-10-12T13:30:00[`

💡 You can apply filters to any sub-property of a given collection

Example : 
`acolytes["name"]='robin'` will filter any `vigilante` resource where at least one item in `acolytes` array with `name` equals to `robin`.

The generic syntax for filtering on in a hierarchical tree
`property["subproperty"]...["subproperty-n"]=<expression>`

you can also use the dot character (`.`).
`property["subproperty"]["subproperty-n"]=<expression>` and `property.subproperty["subproperty-n"]=<expression>`
are equivalent 

## <a href="regex-expression">Regular expression</a>
The library offers a limited support of regular expressions. To be more specific, only bracket expressions are currently supported. 
A bracket expression. Matches a single character that is contained within the brackets. 
For example, `[abc]` matches `a`, `b`, or `c`. `[a-z]` specifies a range which matches any lowercase letter from `a` to `z`.

`BracketExpression`s can be, as any other expressions  combined with any other expressions to build more complex expressions.


## <a href="logic-operators">Logical operators</a>

Logicial operators can be used combine several instances of [IFilter][class-ifilter] together.

### <a href='#' id='and-expression'>And</a>

Use the coma character `,` to combine multiple expressions using logical AND operator 

| Query string         | JSON                                                                                                                                     |
| -------------------- | ---------------------------------------------------------------------------------------------------------------------------------------- |
| `nickname=Bat*,*man` | `{"logic": "and", filters[{"field":"nickname", "op":"startswith", "value":"Bat"}, {"field":"nckname", "op":"endswith", "value":"man"}]}` |


will result in a [IFilter][class-ifilter] instance equivalent to

```csharp
IFilter filter = new MultiFilter
{
    Logic = And,
    Filters = new IFilter[]
    {
        new Filter("nickname", StartsWith, "Bat"),
        new Filter("nickname", EndsWith, "man")
    }
}

<a href='#' id='or-expression'>Or</a>

Use the pipe character | to combine several expressions using logical OR operator Search for vigilante resources where the value of the nickname property either starts with "Bat" or ends with "man"

will result in

IFilter filter = new MultiFilter
{
    Logic = Or,
    Filters = new IFilter[]
    {
        new Filter("nickname", StartsWith, "Bat"),
        new Filter("nickname", EndsWith, "man")
    }
}

<a href='#' id='not-expression'>Not</a>

To negate a filter, simply put a ! before the expression to negate

Search for vigilante resources where the value of nickname property does not starts with "B"

will be parsed into a IFilter instance equivalent to

IFilter filter = new Filter("nickname", DoesNotStartWith, "B");

Expressions can be arbitrarily complex.

"nickname=(Bat*|Sup*)|(*man|*er)"

Explanation :

The criteria under construction will be applied to the value of nickname property and can be read as follow :

Searchs for vigilante resources that starts with Bat or Sup and ends with man or er.

will be parsed into a

IFilter filter = new MultiFilter
{
    Logic = Or,
    Filters = new IFilter[]
    {
        new MultiFilter
        {
            Logic = Or,
            Filters = new IFilter[]
            {
                new Filter("Firstname", StartsWith, "Bat"),
                new Filter("Firstname", StartsWith, "Sup"),
            }
        },
        new MultiFilter
        {
            Logic = Or,
            Filters = new IFilter[]
            {
                new Filter("Firstname", EndsWith, "man"),
                new Filter("Firstname", EndsWith, "er"),
            }
        },
    }
}

The ( and ) characters allows to group two expressions together so that this group can be used as a more complex expression unit.

<a href='#' id='special-character-handling'>Special character handling</a>

Sometimes, you'll be looking for a filter that match exactly a text that contains a character which has a special meaning.

The backslash character (\) can be used to escape characters that will be otherwise interpreted as a special character.

💡 For longer texts, just wrap it between quotes and you're good to go

<a href='#' id='sorting'>Sorting</a>

This library also supports a custom syntax to sort elements.

sort=nickname or sort=+nickname sort items by their nickname properties in ascending order.

You can sort by several properties at once by separating them with a ,.

For example sort=+nickname,-age allows to sort by nickname ascending, then by age property descending.

<a href='#' id='how-to-install'>How to install</a>

1. run dotnet install DataFilters : you can already start building IFilter instances 😉 !
2. install one or more DataFilters.XXXX extension packages to convert IFilter instances to various target.

<a href='#' id='how-to-use'>How to use</a>

So you have your API and want provide a great search experience ?

<a href='#' id='how-to-use-client'>On the client</a>

The client will have the responsability of building search criteria. Go to filtering and sorting sections to see example on how to get started.

<a href='#' id='how-to-use-backend'>On the backend</a>

One way to start could be by having a dedicated resource which properties match the resource's properties search will be performed onto.

Continuing with our vigilante API, we could have

// Wraps the search criteria for Vigilante resources.
public class SearchVigilanteQuery
{
    public string Firstname {get; set;}

    public string Lastname {get; set;}

    public string Nickname {get; set;}

    public int? Age {get; set;}
}

and the following endpoint

using DataFilters;

public class VigilantesController
{
    // code omitted for brievity

    [HttpGet("search")]
    [HttpHead("search")]
    public ActionResult Search([FromQuery] SearchVigilanteQuery query)
    {
        IList<IFilter> filters = new List<IFilter>();

        if(!string.IsNullOrWhitespace(query.Firstname))
        {
            filters.Add($"{nameof(Vigilante.Firstname)}={query.Firstname}".ToFilter<Vigilante>());
        }

        if(!string.IsNullOrWhitespace(query.Lastname))
        {
            filters.Add($"{nameof(Vigilante.Lastname)}={query.Lastname}".ToFilter<Vigilante>());
        }

        if(!string.IsNullOrWhitespace(query.Nickname))
        {
            filters.Add($"{nameof(Vigilante.Nickname)}={query.Nickname}".ToFilter<Vigilante>());
        }

        if(query.Age.HasValue)
        {
            filters.Add($"{nameof(Vigilante.Age)}={query.Age.Value}".ToFilter<Vigilante>());
        }


        IFilter  filter = filters.Count() == 1
            ? filters.Single()
            : new MultiFilter{ Logic = And, Filters = filters };

        // filter now contains our search criteria and is ready to be used 😊

    }
}

Some explanation on the controller's code above :

1. The endpoint is bound to incoming HTTP GET and HEAD requests on /vigilante/search
2. The framework will parse incoming querystring and feeds the query parameter accordingly.
3. From this point we test each criterion to see if it's acceptable to turn it into a IFilter instance. For that purpose, the handy .ToFilter<T>() string extension method is available. It turns a query-string key-value pair into a full IFilter.
4. we can then either :
   • use the filter directly is there was only one filter
   • or combine them using composite filter if there were more than one criterion.

You may have noticed that SearchVigilanteQuery.Age property is nullable whereas Vigilante.Age property is not. This is to distinguish if the Age criterion was provided or not when calling the vigilantes/search endpoint.

Name	Package	Description
DataFilters		provides core functionalities of parsing strings and converting to IFilter instances.
DataFilters.Expressions		adds ToExpression<T>() extension method on top of IFilter instance to convert it to an equivalent System.Linq.Expressions.Expression<Func<T, bool>> instance.
DataFilters Queries		adds ToWhere<T>() extension method on top of IFilter instance to convert it to an equivalent IWhereClause instance.