JSONLogic

Dataflow-rs uses JSONLogic for conditions and data transformations.

Overview

JSONLogic is a way to write rules as JSON. It’s used in dataflow-rs for:

• Workflow Conditions - Control when workflows execute
• Task Conditions - Control when tasks execute
• Map Function - Transform and copy data

Basic Syntax

JSONLogic operations are objects with a single key (the operator) and value (the arguments):

{"operator": [argument1, argument2, ...]}

Data Access

var - Access Data

// Access top-level field
{"var": "data.name"}

// Access nested field
{"var": "data.user.profile.email"}

// Access array element
{"var": "data.items.0"}

// Default value if missing
{"var": ["data.optional", "default value"]}

Context Structure

In dataflow-rs, the context available to JSONLogic is:

{
    "data": { ... },
    "metadata": { ... },
    "temp_data": { ... }
}

Access fields with:

{"var": "data.field"}
{"var": "metadata.type"}
{"var": "temp_data.intermediate"}

Comparison Operators

Equality

{"==": [{"var": "data.status"}, "active"]}
{"===": [{"var": "data.count"}, 0]}  // Strict equality
{"!=": [{"var": "data.status"}, "deleted"]}
{"!==": [{"var": "data.count"}, null]}  // Strict inequality

Numeric Comparisons

{">": [{"var": "data.age"}, 18]}
{">=": [{"var": "data.score"}, 60]}
{"<": [{"var": "data.price"}, 100]}
{"<=": [{"var": "data.quantity"}, 10]}

Between

{"<=": [1, {"var": "data.x"}, 10]}  // 1 <= x <= 10
{"<": [1, {"var": "data.x"}, 10]}   // 1 < x < 10

Boolean Logic

and, or, not

{"and": [
    {">=": [{"var": "data.age"}, 18]},
    {"==": [{"var": "data.verified"}, true]}
]}

{"or": [
    {"==": [{"var": "data.status"}, "active"]},
    {"==": [{"var": "data.status"}, "pending"]}
]}

{"!": {"var": "data.disabled"}}

Truthy/Falsy

// Check if value is truthy (not null, false, 0, "")
{"!!": {"var": "data.email"}}

// Check if value is falsy
{"!": {"var": "data.deleted"}}

Conditionals

if-then-else

{"if": [
    {">=": [{"var": "data.score"}, 90]}, "A",
    {">=": [{"var": "data.score"}, 80]}, "B",
    {">=": [{"var": "data.score"}, 70]}, "C",
    "F"
]}

Ternary

{"if": [
    {"var": "data.premium"},
    "VIP Customer",
    "Standard Customer"
]}

String Operations

cat - Concatenation

{"cat": ["Hello, ", {"var": "data.name"}, "!"]}

substr - Substring

{"substr": [{"var": "data.text"}, 0, 10]}  // First 10 characters
{"substr": [{"var": "data.text"}, -5]}     // Last 5 characters

in - Contains

// Check if substring exists
{"in": ["@", {"var": "data.email"}]}

// Check if value in array
{"in": [{"var": "data.status"}, ["active", "pending"]]}

Numeric Operations

Arithmetic

{"+": [{"var": "data.a"}, {"var": "data.b"}]}
{"-": [{"var": "data.total"}, {"var": "data.discount"}]}
{"*": [{"var": "data.price"}, {"var": "data.quantity"}]}
{"/": [{"var": "data.total"}, {"var": "data.count"}]}
{"%": [{"var": "data.n"}, 2]}  // Modulo

Min/Max

{"min": [{"var": "data.a"}, {"var": "data.b"}, 100]}
{"max": [{"var": "data.x"}, 0]}  // Ensure non-negative

Array Operations

merge - Combine Arrays

{"merge": [
    {"var": "data.list1"},
    {"var": "data.list2"}
]}

map - Transform Array

{"map": [
    {"var": "data.items"},
    {"*": [{"var": ""}, 2]}  // Double each item
]}

filter - Filter Array

{"filter": [
    {"var": "data.items"},
    {">=": [{"var": ""}, 10]}  // Items >= 10
]}

reduce - Aggregate Array

{"reduce": [
    {"var": "data.items"},
    {"+": [{"var": "accumulator"}, {"var": "current"}]},
    0  // Initial value
]}

all/some/none

{"all": [{"var": "data.items"}, {">=": [{"var": ""}, 0]}]}
{"some": [{"var": "data.items"}, {"==": [{"var": ""}, "special"]}]}
{"none": [{"var": "data.items"}, {"<": [{"var": ""}, 0]}]}

Try It

Common Patterns

Safe Field Access

// Default to empty string
{"var": ["data.optional", ""]}

// Check existence first
{"if": [
    {"!!": {"var": "data.optional"}},
    {"var": "data.optional"},
    "default"
]}

Null Coalescing

{"if": [
    {"!!": {"var": "data.primary"}},
    {"var": "data.primary"},
    {"var": "data.fallback"}
]}

Type Checking

// Check if string
{"===": [{"typeof": {"var": "data.field"}}, "string"]}

// Check if array
{"===": [{"typeof": {"var": "data.items"}}, "array"]}

Best Practices

1. Use var Defaults - Provide defaults for optional fields
2. Check Existence - Use !! to verify field exists before use
3. Keep It Simple - Complex logic may be better in custom functions
4. Test Expressions - Use the playground to test JSONLogic before deploying