spleen
v1.3.0
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Dynamic filter expression parsing, formatting, and abstractions for web APIs.
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spleen
Easily add dynamic filtering to your application.
Say we have a REST endpoint to a collection, and we need to provide a way for users to specify filter criteria when querying this collection. This is a fairly common problem, and there are a couple of challenges that come out of this scenario. How is the filter expression formatted when it's passed in via an HTTP request? How do we pass this expression to our domain logic and data access layers without leaking implementation details? The spleen
module seeks to solve these challenges.
Contents
Usage
Add spleen
to your package.json
file's dependencies
:
$ npm install spleen -S
You can then parse spleen
filter expression strings:
const spleen = require('spleen');
const expression = '/foo eq "bar" and /baz gt 42';
const filter = spleen.parse(expression);
Or define filter graphs directly (which is more efficient from a runtime performance perspective):
const spleen = require('spleen');
const Clause = spleen.Clause;
const Filter = spleen.Filter;
const filter = Filter
.where(
Clause
.target('/foo')
.eq()
.target('/bar')
)
.and(
Clause
.target('/baz')
.gt()
.literal(42)
);
const src = {
foo: 'a',
bar: 'a',
baz: 100
};
const match = filter.match(src);
console.log(match); // true
Spleen Expressions
A spleen
filter expression is a string that can be used as input from external sources, such as in URL query strings.
Grammar
Expression strings use infix notation to maximize read and writability by humans, and follows the form:
[<group>]
<clause>
<subject:target|literal/>
<verb:compare|range|array|search/>
<object:target|literal|range|array|search/>
</clause>
[</group>]
[<conjunctive/> <clause/>] ...
<group> ... </group>
(optional) A logical grouping of filter clauses.<clause/>
: (required) a statement that describes a filter condition. Each statement must follow a specific form:<subject/>
: (required) the thing you are filtering on. A<subject>
can be expressed in one of two ways:<subject:target/>
: a reference to a field on the data you are filtering.<subject:literal/>
: a static value used in the filter condition.
<verb/>
: (required) the operator you are using to perform the comparison. Operators can be one of several types:<verb:compare/>
: a simple comparison between two values.<verb:range/>
: determines whether or not the<subject/>
is within a range of values.<verb:array/>
: determines whether or not the<subject/>
is in an array.<verb:search/>
: determines whether or not the<subject/>
matches a certain search criteria.
<object/>
: (required) the value used to filter data agains the<subject/>
. There are several types of<object/>
values that can be used, however, the type is dependent upon the preceding operator type.<object:target/>
: a reference to a field. This<object/>
type can only be used when the preceding operator is of type<verb:compare/>
or<verb:array/>
.<object:literal/>
: a static value. This<object/>
type can only be used when the preceding operator is of type<verb:compare/>
.<object:range/>
: two literal values that<subject/>
can be between (including the two edge values). This<object/>
type can only be used when the preceding operator is of type<verb:range/>
.<object:array/>
: an array value. This<object/>
type can only be used when the preceding operator is of type<verb:array/>
.<object:search/>
: a string matching expression used to evaluate whether or not<subject/>
is a match.
<conjunctive/>
: (optional) a logical joining of multiple filter conditions.
Syntax
The following is a list of all possible values for the various types of terms used in a spleen
expression.
<group>
:(
: opens a group.
</group>
:)
: terminates a group.
<subject:target/>
:/json/pointer
: a field reference in RFC 6901 format.
<subject:literal/>
:"..."
: a string literal. All values are contained with"
characters (U+0022).12345.67890
: a number value that can be either an integer or floating point.true
orfalse
: a Boolean value.nil
: a null literal value.
<verb:compare/>
:eq
: equal to.neq
: not equal to.gt
: greater than.gte
: greater than or equal to.lt
: less than.lte
: less than or equal to.
<verb:range/>
:between
: is between two other values.nbetween
: is not between two other values.
<verb:array/>
:in
: is in array.nin
: is not in array.
<verb:search/>
:like
: matches a search string pattern.nlike
: does not match a search string pattern.
<object:target/>
:/json/string
: a reference expression in RFC 6901 format.
<object:literal/>
:"..."
: a string literal. All values are contained with"
characters (U+0022).12345.67890
: a number value that can be either an integer or floating point.true
orfalse
: a Boolean value.
<object:range/>
:{literal},{literal}
: two literal values (string or number) delimited by a comma.
<object:array/>
:[{literal}]
: an array of literal values (string, number, or Boolean) delimited by a comma.
<object:search/>
:*match_pattern*"
: a set of characters and wildcards used for matching string patterns. Wildcards include:*
: match zero or more of any character. Most like pattern formats use a%
for this purpose. Thespleen
module uses*
to be more URL-friendly._
: match one of any character.\
: escape a reserved wildcard character.
Terms are generally delimited by a SPACE
character (U+0020). The exception being group initiator and terminator characters, which can abut other terms without a delimiter.
Examples
Subfield bar
of field foo
is equal to string literal "baz"
.
/foo/bar eq "baz"
Field bar
of field foo
is not equal to string literal "baz"
, and field qux
is greater than or equal to 42.
/foo/bar neq "baz" and /qux gte 42
Field bar
of field foo
is equal to nil
(null
).
/foo/bar eq nil
The conditions field bar
of field foo
is not equal to string literal "baz"
and field qux
is greater than or equal to 42 must be true, or the field quux
must start with "Hello"
.
(/foo/bar neq "baz" and /qux gte 42) or /quux like "Hello*"
The value of field foo
should not be in the array of values 42
, "bar"
, and "baz"
.
/foo nin [42,"bar","baz"]
The value of field foo
should be in the array value of field bar
.
/foo in /bar
The value of field foo
is greater than or equal to 0
or less than or equal to 42
.
/foo between 0,42
The primary use case for spleen
expressions is to accept a filter condition from an external source. For example, as a query parameter on a request to a REST-based API:
GET api/v1/organizations?filter=/customerId+eq+"123"+and+/name+like+"*awesome*"
Building Filters
A filter graph can also be built in code using the Filter
class' fluent API:
const spleen = require('spleen');
const Filter = spleen.Filter;
const Operator = spleen.Operator;
const Range = spleen.Range;
const Target = spleen.Target;
const filter = Filter
.where(
Clause
.target('/foo')
.eq()
.literal('bar')
)
.and(
Clause
.target('/baz')
.between()
.range('a', 'm')
)
.andGroup(
Filter
.where(
Clause
.target('/qux')
.neq()
.literal(42)
)
.or(
Clause
.target('/quux')
.lt()
.literal(42)
)
);
API
Module
The primary interface exposes all of the classes needed to build spleen
filters.
Properties
spleen.Clause
gets a reference to theClause
class.spleen.errors
: gets an object with references to all error types thrown by the module:MatchError
: an error thrown whenmatch()
is called on an invalidFilter
. Generally, this should never happen.ParserError
: an error thrown when aspleen
expression string cannot be parsed. This error'sdata
property is the numeric index of the invalid token encountered by the parser.
spleen.Filter
: gets a reference to theFilter
class.spleen.Like
: gets a reference to theLike
class.spleen.parse(value)
parses a string, and converts it into an instance ofFilter
.Parameters
value
: a string representing aspleen
expression.
This method returns an object with the following keys:
error
: ifvalue
was in invalidspleen
expression, this key will be an instance ofParserError
with additional information about why the failure occured.filter
: if parsing was successful, this key is an instance ofFilter
.success
: a Boolean value indicating whether or not parsing was successful.
spleen.Range
: gets a reference to theRange
class.spleen.Target
: gets a reference to theTarget
class.
Class: Clause
Represents a single Boolean expression. An instance of Clause
is built using the methods described below, and can only be usable within a Filter
once they are complete, valid expressions. Meaning, they must have a subject, verb, and object (as described in "Grammar").
Properties
subject
: gets the subject value for theClause
. This will always be either an instance ofTarget
, a string, number, or Boolean.operator
: gets the verb portion of theClause
. This is an operator which is an object with the keytype
. Thetype
property can have a value ofeq
,neq
,gt
,gte
,lt
,lte
,in
,nin
,between
,nbetween
,like
, ornlike
.object
: the object portion of theClause
. The possible values for this property are constrained by the value ofoperator
.If
operator
iseq
,neq
,gt
,gte
,lt
, orlte
, thenobject
can be an instance ofTarget
, a string, number, or Boolean.If
operator
isin
ornin
, thenobject
can be an array of strings, numbers, and Booleans.If
operator
isbetween
ornbetween
thenobject
can be an instance ofRange
.If
operator
islike
ornlike
thenobject
can be an instance ofLike
.
Methods
Many of the methods for
Clause
only become available after a certain method has been called. All instances ofClause
are constructed using one of its factory methods:Clause.target(value)
: sets the subject of theClause
to an instance ofTarget
.Parameters
value
: (required) a JSON-pointer string.
Clause.literal(value)
sets the subject of theClause
to a literal.Parameters
value
: (required) a string, number, or Boolean value.
Once the
subject
of theClause
has been set, available methods begin branching. Calling one method itself unavailable, while also enabling methods in the following fashion:Comparison
Clause.prototype.eq()
: sets the operator toeq
(equal to).Clause.prototype.neq()
: sets the operator toneq
(not equal to).Clause.prototype.gt()
: sets the operator togt
(greater than).Clause.prototype.gte()
: sets the operator togt
(greater than or equal to).Clause.prototype.lt()
: sets the operator tolt
(less than).Clause.prototype.lte()
: sets the operator tolte
(less than or equal to).
Children:
Clause.prototype.target(value)
: ets the object of theClause
to an instance ofTarget
.Parameters
value
: (required) a JSON-pointer string.
Clause.prototype.literal(value)
: sets the object of theClause
to a literal.Parameters
value
: (required) a string, number, or Boolean value.
Array
Clause.prototype.in()
: sets the operator toin
(in array).Clause.prototype.nin()
: sets the operator tonin
(not in array).
Children:
Clause.prototype.array(value)
: sets theobject
of theClause
to an array.Parameters
value
: (required) an array of strings, numbers, and Booleans.
Range
Clause.prototype.between()
: sets the operator tobetween
(between two values).Clause.prototype.nbetween()
: sets the operator tonbetween
(not between two values).
Children:
Clause.prototype.range(lower, upper)
: a range of values that the value of subject should fall between.Parameters
lower
: (required) a string or number representing the lower portion of the range expression.upper
: (required) a string or number representing the upper portion of the range expression.
Search
Clause.prototype.like()
: sets the operator tolike
(like a string pattern)Clause.prototype.nlike()
: sets the operator tonlike
(not like a string pattern)
Children:
Cluase.prototype.pattern(value)
: sets the object to a string matching pattern. This method wrapsvalue
in an instance ofLike
.Parameters
value
: (required) a string value using string matching the wildcards described in "Syntax."
Class: Filter
Represents the graph structure of a spleen
filter.
Properties
Filter.prototype.fields
: gets an array of all field references used in the filter.Filter.prototype.statements
: gets an array of all nodes within the filter graph. Each entry is an object that consists of the keys:conjunctive
: a string that specifies how a statement is conjoined with the previous statement. This can be either an empty string,and
, oror
.value
: the value of the statement. This can be either an instance ofClause
orFilter
. Ifvalue
is an instance ofFilter
then the statement is interpreted as a group.
Methods
Filter.group(filter)
: factory method for creating a new filter graph, where the first statement is a set of clauses nested in a group.Parameters
filter
: (required) an instance ofFilter
to nest in a group.
This method returns an instance of
Filter
.Filter.where(clause)
: factory method for creating new filter graphs, where the first statement is a clause.Parameters
clause
: (required) an instance ofClause
to use as the first statement in theFilter
.
This method returns an instance of
Filter
.Filter.prototype.and(clause | filter)
: appends an instance ofClause
or the statemetns within aFilter
to theFilter
's list of statements using an "and" conjunctive.Parameters
clause
: (required) an instance ofClause
.
...or...
filter
(required) an instance ofFilter
. If this overload is called, all of the statements for the given filter are concatonated onto the end of theFilter
instance's statements. All statements appended on are treated as individual statements, and not a single group. The first statement in the joined filter is conjoined with an "and."
This method returns the
Filter
instance.Filter.prototype.andGroup(filter)
: ands an instance ofFilter
as a single statement evaluated as a group. The statement is joined to the previous statement with an "and."Parameters
filter
: (required) the instance ofFilter
to add as a group statement.
This method returns the
Filter
instance.Filter.prototype.match(value)
: determines whether or not theFilter
matches a given value.Parameters
value
: (required) the value to be matched.
This method returns a Boolean value indicating whether or not there was a match.
Filter.prototype.or(clause | filter)
: appends an instance ofClause
or the statemetns within aFilter
to theFilter
's list of statements using an "or" conjunctive.Parameters
clause
: (required) an instance ofClause
.
...or...
filter
(required) an instance ofFilter
. If this overload is called, all of the statements for the given filter are concatonated onto the end of theFilter
instance's statements. All statements appended on are treated as individual statements, and not a single group. The first statement in the joined filter is conjoined with an "or."
This method returns the
Filter
instance.Filter.prototype.orGroup(filter)
: ands an instance ofFilter
as a single statement evaluated as a group. The statement is joined to the previous statement with an "or."Parameters
filter
: (required) the instance ofFilter
to add as a group statement.
This method returns the
Filter
instance.Filter.prototype.prioritize(priorities [, options] | strategy)
: creates a shallow copy of theFilter
instance, and reorders all statements to align with a given list of field targets that is ordered by priority.Reordered statements cannot always be made to be in perfect prioritization order. This method will always compute a
Filter
instance that is logically the same as the original. For example...- Given the expression
/bar eq 2 or /baz eq 3 and /foo eq 1
- A priority list of
['/foo', '/bar', '/baz']
- And a conjuction precedence of
and
(the default) - The result will be
/foo eq 1 and /baz eq 3 or /bar eq 2
Parameters
priorities
: (required) an array of field targets in RFC 6901 format. The array should be in priority order, from most important (index 0) to least important.options
: (optional) an object with the following keys:precedence
: (optional) a string that can be eitherand
oror
(case insensitve). This dictates how an expression should be evaluated, and, consequently, how statements within aFilter
can be reoranized.
...or...
strategy
: (required) an instance ofPrioritizeStrategy
.
This method returns an object with the following fields:
filter
: the newFilter
instance.
- Given the expression
Filter.prototype.toString(urlEncode)
: returns aspleen
filter expression.Parameters
urlEncode
: (optional) a Boolean indicating whether or not the string should be URL encode.
This method returns a Boolean indicating whether or not that there was a match.
Class: Like
Represents a "like" string matching expression. This clause is used as the "object" in "search" comparisons.
Properties
Like.prototype.value
: gets the string value of the "like" expression.
Methods
Like.prototype.match(value)
: compares a given string agains the like expression.Parameters
value
: a string value to match.
This method returns a Boolean.
Like.prototype.toRegex()
: converts the Like pattern to a compatible regular expression. This method returns in an instance ofRegExp
.Like.prototype.toRegexString()
: converts the Like pattern to a compatible regular expression string. This method returns a string.
Class: PrioritizeStrategy
A cache of computed information used to prioritize statements in a Filter
instance.
Methods
PrioritizeStrategy.create(priorities [, options])
: builds aPrioritizeStrategy
.Parameters
priorities
: (required) an array of field targets in RFC 6901 format. The array should be in priority order, from most important (index 0) to least important.options
: (optional) an object with the following keys:precedence
: (optional) a string that can be eitherand
oror
(case insensitve). This dictates how an expression should be evaluated, and, consequently, how statements within aFilter
can be reoranized.
Class: Range
Represents a range of two values. This is class is used as the "object" in "range" comparisons.
Properties
Range.prototype.lower
: the lower value in the range.Range.prototype.upper
: the upper value in the range.
Methods
Range.between(value)
: indicates whether or not the value falls within the range defined bylower
andupper
.Parameters
value
: (required) a string or number value to evaluate.
This method returns a Boolean indicating whether or not that there was a match.
Class: Target
Represents a reference to a field on an object being filtered.
Properties
Target.prototype.field
: gets the field being referenced. This is useful if the target path includes an array index. Field names are expressed as strings in JSON pointer format. This differs from the actual target value in cases where a field index is used in the path. For example,/foo/0/bar
references fieldbar
of index item0
of fieldfoo
. In this case, the value offield
would be/foo
.Target.prototype.path
: gets an in-order array of strings and numbers that represent how to traverse an object and its sub objects to find a value. A string is a field reference, and a number is an index lookup (for example, in an array).
Methods
Target.jsonPointer(value)
: parses a JSON pointer value.Parameters
value
: (required) the JSON pointer to parse.
This method returns an instance of
Target
representing the JSON pointer.
Conversions
One of the goals of spleen
is to provide a high-level abstraction for filter expressions. The idea is to provide a DSL that can be consistently used across application layers without leaking implementation details. Each layer in the application is then responsible for consuming a spleen
filter expression in its own way.
In the case of a data access layer, this typically means converting a Filter
instance into some flavor of SQL. For now, there is a single plugin available for accomplishing this end: spleen-n1ql (for now).
Motivation
Representing dynamic complex filter expressions is a fairly common problem for API developers. There are a variety of methods commonly used by teams, and they all have their pros and cons...
Use the query string to pass in filter criteria. Pros: Very easy to implement. Universally understood. Cons: Query strings have no native way of specifying comparison operators. Difficult to make APIs idiomatic.
Expose the underlying query language used by your database. Pros: Can provide a lot of power. Little to no effort to implement. Cons: Leaks internal implementation details. Difficult to secure.
Build a custom filter dialect and parser. Pros: Greater control over the software. Cons: Teams often make these tools domain-specific. Complex and time-consuming to build. Closed-source solutions do not benefit from a larger community of people and companies testing and contributing to the project.
Use frameworks for querying languages such as GraphQL and OData. Pros: Very robust. Support for full ad-hoc querying. Cons: Represents a broader system design. May not be practical for use in existing systems built on an intent-based design (like REST). Built around opinionated frameworks that can be complicated to implement. Limited ability to optimize ad-hoc queries at runtime, and fully take advantage of database indexes. Poorly designed user-specified queries can be used as a vector for DoS attacks.
The spleen
module addresses these challenges wtih the following goals in minds:
No strong opinions. The
spleen
module is a library, and does not insist upon any broader design patterns.Can be implemented with minimal effort.
Enables complex filter logic with support for a variety of comparison operators, functions, and conjunctions.
Provides an abstraction around the issue of dynamically filtering data.
Domain agnostic.
Allows API endpoints to utilize a single query parameter for filtering. This makes your APIs more idiomatic, and your code simpler.
Ability to prioritize user-defined filter clauses. This allows implementers to generate efficient, index-aware queries.
Provide plugins that help make database query commands secure.