Multi-Attribute Filtering on Lookup Schemas: A Practical Guide

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When working with lookup schemas, you may often need to filter a list of objects based on more than one attribute. This guide explains how to perform multi-attribute filtering on lookup schemas using nested filter() functions. This is especially useful when you need to narrow down a list of objects based on more than one condition—such as filtering products in a shopping cart by both ID and color.

When to Use This Pattern 

We should use nested filtering when: 

• You need to apply multiple independent filtering criteria on a list within a lookup schema. 
• You want to avoid complex expressions that may lead to expression parsing errors in your event processing system. 

 Where to write the expression 

1. Open your journey in AJO. 
2. Select the condition where you want to apply the multi-attribute filter. 
3. In the configuration panel, look for the "Expression" section. 
4. Click "Edit" (or the pencil icon) to open the expression editor. 
5. Enter your custom filter expression and save changes. 

Common Pitfalls 

Avoid the following mistakes when applying filters inside a lookup schema: 

Misusing .all() with Nested Fields - A common mistake is trying to filter the array by a lookup field inside your `.all(…)` clause within `@event`, or attempting to use the `and` operator inside `.all(…)`. These patterns can cause the expression engine parser to throw the following error: 

BadRelatedSchemaException: Could not resolve schema id from schema identifier because event was not defined. 

 
Solution: Nested filter() Functions 

Use nested filter functions with the following syntax: 

filter(filter(<parameters>)) 

filter( 
      filter(listToFilter, keyAttributeName1, keyValueList1), 
      keyAttributeName2, keyValueList2 
)

Where parameters are defined as: 

Parameter	Type	Description
listToFilter	listObject	List of objects to be filtered. It must be a field reference.
keyAttributeName	string	Attribute name in the objects of the list, used as key for filtering.
keyValueList	list	Array of key values for filtering.

Examples 

Example 1 : Suppose we are using a lookup schema that contains a list of products in a cart. Each product has attributes like `id`, `name`, `price`, and `color`. We want to filter this list to include only products that: 

1. Have an ID in the set: ["product2", "product3", "product4", "product5"] 
2. Have a color either "blue" or "red" 
   

 Input product list: 

[ 
    { "id": "product1", "name": "the product 1", "price": 20, "color": "red"}, 
    { "id": "product2", "name": "the product 2", "price": 30, "color": "blue" }, 
    { "id": "product3", "name": "the product 3", "price": 50, "color": "red" }, 
    { "id": "product4", "name": "the product 4", "price": 60, "color": "yellow" } 
] 

  Use the following expression to perform multi-attribute filtering: 

filter( 
  filter(@event{cart_lookup.productListItems."@(<schema>)".taxonomy}, 
    "id",  
   ["product2", "product3", "product4", "product5"] 
  ), 
  "color",  
  ["blue", "red"] 
) 

This expression returns a listObject containing the two objects with IDs "product2" and "product3". 

Example 2: Inventory alert (low stock AND preferred colors) 

filter( 
  filter(@event{inventoryLookup.items},"unitsAvailable",[0,1,2,3,4,5]), 
  "color", 
  ["green","blue"] 
) 

Returns only items where stock is ≤5 and whose color is green or blue. Great for “back-in-stock” or low-stock push alerts. 
 
 
Example 3: Premium-SKU up-sell (price ≥ 100 AND brand in list) 

filter( 
  filter(@event{cart.productListItems},"price", range(100,9999)), 
  "brand", 
  ["AcmePro","EliteGear"] 
) 

Use when you want to trigger an in-journey branch only if both price is high and the brand is on a VIP list.  (Here range() is any list of numbers—you can pre-build it, e.g. [100,101,…])