RSQL for MongoDB-Filter

RSQL is a query language based on FIQL (Feed Item Query Language). It's an URI-friendly syntax and therefore well suited for API's.

The language

Basics

RSQL supports multiple comparison operations. The following table gives an overview and a matrix that shows which literals can be used with the corresponding operators.

Operator	Description	Oid	Bool	String	Number	Array	Example
==	equal	✔️	✔️	✔️	✔️	✔️	_id==$oid(ABCDEF012345) title=="Hello World"
!=	not-equal	✔️	✔️	✔️	✔️	✔️	status!="pending"
=gt=	greater-than	❌	❌	❌	✔️	❌	probability=gt=0.5
=ge=	greater-than-qual	❌	❌	✔️	❌	age=ge=18
=lt=	less-than	❌	❌	❌	✔️	❌	probability=lt=0.5
=le=	less-than-equal	❌	❌	❌	✔️	❌	high=le=1.60
=sw=	starts with	❌	❌	✔️	❌	❌	table=sw="DB_"
=ew=	ends with	❌	❌	✔️	❌	❌	file=ew=".jpg"
=in=	contains	❌	❌	❌	❌	✔️	log_level=in=("panic","error","warning")
=out=	not-contains	❌	❌	❌	❌	✔️	grade=out=(1,2)

NOTE: equal and not equal can also be used to check if array contains an single element. E.g. document has {roles: ["dev","maintainer","admin"]}, than you can check if has admin role by using roles=="admin".

Multiple comparisons can be combined with composite operators:

Operator	Description	Example
;	Logical AND	gender=="female";age=ge=30
,	Logical OR	level=="senior",level=="expert"

For more advanced queries, context may be helpful. They can be used by round brackets e.g. (expression;expression),(expression;expression). A more accurate example could be a binary XOR (only a or b is 1) (a==0;b==1),(a==1;b==0).

Example

For API

import (
	"github.com/StevenCyb/go-mongo-tools/mongo/rsql"

	"go.mongodb.org/mongo-driver/mongo/options"
)

func ListHandler(w http.ResponseWriter, r *http.Request) {
  queryExpressionString := r.URL.Query().Get("query")

  parser := rsql.NewParser(nil)
  queryExpression, err := parser.Parse(queryExpressionString)
  // ...

  coll.Find(r.Context(), queryExpression)
  // ...
}

For API with policy

This parser supports two types of policies:

1. WHITELIST_POLICY -> disallow everything except given fields
2. BLACKLIST_POLICY -> allow everything except given fields

import (
	"github.com/StevenCyb/go-mongo-tools/mongo/rsql"
	"github.com/StevenCyb/go-mongo-tools/tokenizer"

	"go.mongodb.org/mongo-driver/mongo/options"
)
// ...

  queryExpressionString := r.URL.Query().Get("query")

  parser := rsql.NewParser(
    // just allow expression with
    // "first_name", "last_name" and "age"
    tokenizer.NewPolicy(
      tokenizer.WHITELIST_POLICY,
      "first_name", "last_name", "age",
    )
  )
  queryExpression, err := parser.Parse(queryExpressionString)
  // ...

  coll.Find(r.Context(), queryExpression)
  // ...