Write custom logic with UDFs

Fauna supports user-defined functions (UDFs) for encapsulating business logic as manageable and maintainable resources. UDFs are equivalent to SQL stored procedures.

A UDF is an anonymous function with the same calling syntax as the JavaScript arrow function expression.

UDFs support JavaScript’s rest parameter syntax (…​). See Rest parameters.

See User-defined functions in the migration document for FQL v10 and FQL v4 UDF interoperability.

You define UDFs in Fauna Schema Language (FSL) as a schema. You manage schemas using the Fauna Dashboard or the Fauna CLI.

The examples in this tutorial use the Fauna Dashboard and Fauna’s demo data.

Create a UDF and call it

This example UDF calculates the circumference of a circle.

  1. In the Dashboard, open the Demo database and add the following getCircumference() function:

    function getCircumference(radius) {
  2 * Math.PI * radius
}

  2. Call the UDF by its name, passing a parameter:

    getCircumference(12)
    75.39822368615503

  3. To view the UDFs for the database, call Function.all():

    Function.all()
    {
  data: [
    {
      name: "inventory",
      coll: Function,
      ts: Time("2099-04-09T17:39:57.983Z"),
      role: "server",
      body: <<-END
        (name) => {
          Product.byName(name) {
            name: .name,
            description: .description,
            quantity: .quantity
          }
          
        }
      END
    },
    ...
    {
      name: "getCircumference",
      coll: Function,
      ts: Time("2099-04-09T17:39:57.983Z"),
      body: "radius => 2 * Math.PI * radius"
    }
  ]
}

Use UDFs to store a query

You can also use UDFs to store common queries for reuse.

The following example uses the Product collection from Fauna’s demo data.

  1. In the Dashboard, create a productsByNameAndQuantity() function that:

    • Accepts the name and quantity parameters.

    • Uses the Product collection’s byName index to:

      • Search for products with the provided name.

      • Filter matching products to those with a quantity less than or equal to the provided quantity.

    • Returns the name, description, and quantity of matching products.

    function productsByNameAndQuantity(name, quantity) {
  Product.byName(name, { from: quantity }) {
    name: .name,
    description: .description,
    quantity: .quantity
  }
}

  2. Call the function with a name of limes and a quantity of 50:

    productsByNameAndQuantity("limes", 50)

    The query returns products named limes that have a quantity of 50 or less:

    {
  data: [
    {
      name: "limes",
      description: "Organic, 16 oz bag",
      quantity: 45
    },
    {
      name: "limes",
      description: "Conventional, 16 oz bag",
      quantity: 22
    }
  ]
}

Delete a UDF

To delete a function, remove its schema using the Fauna Dashboard or Fauna CLI. With the CLI:

  1. Delete the .fsl file for the function schema from your schema directory.

  2. Run fauna schema push to push the updated schema directory to Fauna. This deletes the function.

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