Filtering on Item Property

At times, you may want to have recommendations on items satisfying certain criteria: a price range, the release year of a movie, a minimal popularity, some internal business rule… Filters are provided for this task, enabling your client to dynamically preselect items based on their properties. They are a type of business rules.

Naturally, the richer the items properties, the better the filter, but that’s only the tip of the iceberg since this feature is useful at two different levels:

• You can create server-side business rules, such as displaying only new TV-shows in some sections of your app.

• You can hand over control to your end user with buttons and switches, so they can configure themselves what they see. Think price range, clothes’ color, category, brand or platform.

Keep in mind that each filter applies to only one item-property; you can then combine multiple filters together, resulting in the intersection of all.

Below, we first present the syntax of filters (the two ways to use them) before moving on to their logic to see what each filter operator does and how to combine them.

Filter Syntax

There are two equivalent ways to format a filter: either using a JSON object or using a URL-compatible string.

JSON Object Format

The JSON object defining a filter is formed by the following fields:

• property_name: the item-property name on which you want to filter

• op: the filter operator (case insensitive). Available operators are defined in Filter Logic below

• value: the optional value for the operator.

  Depending on the operator, this field is either omitted or compulsory. When required, the value type also depends on the item-property type (scalar/string) and on the operator (single scalar/string or list thereof), please see the respective types in the table below.

  The value in filters can reference the properties of the source item or the source user. For instance to filter the similar items recommendations on only items of the same category of the source item. For this value must be a nested object with fields:

  • type: either "item_property" or "user_property"

  • value: the name of the property

URL-Compatible Format

The equivalent syntax is also allowed. This is particularly useful to send the filters as URL query parameters.

<PROPERTY_NAME>:<OP>

for operators without value, or

<PROPERTY_NAME>:<OP>:<VALUE>

for operators with a value.

Do remember to use percent-encoding when using reserved characters as values.

Note that nested object values are not available in URL-Compatible format.

Examples

price smaller than a number

For instance this filter enforces recommendations of only items with a price strictly less than 10.

URL-string version: price:lt:10.

Object version:

{
  "property_name": "price",
  "op": "lt",
  "value": 10
}

tags in a given list

This other filter enforces recommendations of only items with either the tag family or the tag fiction.

URL-string version: tags:in:family,fiction.

Object version:

{
  "property_name": "tags",
  "op": "in",
  "value": ["family", "fiction"]
}

at least one actor

This third filter enforces recommendations of only items which contain at least a value in the property actors.

URL-string version: actors:NotEmpty (operators are case-insensitive).

Object version:

{
  "property_name": "actors",
  "op": "NotEmpty"
}

category in the selected categories of the user

This filter for profile-to-items recommendations enforces recommendations of only items with category in the list of the user’s selected_categories. Here selected_categories is a repeated user property for which the value will be evaluated at runtime.

URL-string version not available for nested value.

Object version:

{
  "property_name": "category",
  "op": "in",
  "value": {
    "type": "user_property",
    "value": "selected_categories"
  }
}

price higher that the price of the source item

This filter for item-to-items recommendations enforces recommendations of only items with price higher than the price of the source item.

URL-string version not available for nested value.

Object version:

{
  "property_name": "price",
  "op": "gt",
  "value": {
    "type": "item_property",
    "value": "price"
  }
}

Filter Logic

You will find below the table of all operators and a detailed description of the filtering logic.

Operators Table

The API implements the following operators.

Operator	Value	Description	Quantifier for Repeated Property
eq	scalar	equal to value	exists
lt	scalar	strictly less than value	exists
lte	scalar	less or equal to value	exists
gt	scalar	strictly greater than value	exists
gte	scalar	greater or equal to value	exists
in	list	equal to one of the values	exists
neq	scalar	not equal to value (or null)	forall
notin	list	not equal to any of the values (or null)	forall
notempty	none	not null	exists

Note that not all operators are available for all property types. For instance floating point properties suffer from precision issues and therefore cannot be filtered using equality. Please refer to Property Types to find if an operator is available.

Quantifier for Repeated Property

For repeated properties, such as a list of many tags, most operators follow the exists set quantifier. This means that the API will return items where at least one of the repeated values satisfies the operator.

For instance by using the filter tags:eq:family the API may return items with {"tags": ["action", "family"]} or {"tags": ["family"]}, but will not return any item with {"tags": []} or {"tags": ["action"]}.

Two operators do not follow this logic and instead implement the forall set quantifier: neq and notin. For these operators all repeated values must satisfy the operator.

For instance by using the filter tags:notin:family,drama the API may return items with {"tags": []} or {"tags": ["action", "comedy"]}, but will not return any item with {"tags": ["action", "family"]} or {"tags": ["action", "drama"]}.

This logic is only relevant for repeated properties because on a set of size 1, exists and forall are equivalent.

Combining Rules

By combining multiple filters you can achieve complex business rules.

Multiple Filters

When using multiple filters, the API will return items that satisfy all filters.

For instance using both price:gte:4 and price:lte:10 together will return only items with a price between 4 and 10.

Putting Everything Together

By default the operators neq or notin also return items with empty sets for this property. You may want to also exclude these items without the property. You can achieve this by adding a notempty filter on the same property.

When using multiple filters on the same repeated property, each filter is considered independently. Combining all the above logic is a great tool to generate complex business rules, but it can also produce un-intuitive filtering with repeated integers. For instance, an item with {"scores": [1, 2, 3, 4]} satisfies the filters scores:gt:3 & scores:lt:2.