with-default-read

Use with-default-read to read a row from a specified table for a given key and bind columns according to provided bindings. If the row is not found, the function reads columns from a default object with matching key names.

Basic syntax

To read a row from a table with default values and bind columns according to the provided binding, use the following syntax:

(with-default-read table key default bindings)

Arguments

Use the following arguments to specify the table, key, defaults, bindings, and body for execution using the with-default-read Pact special form.

Argument	Type	Description
table	table: <{row}>	Specifies the table from which to read the row.
key	string	Specifies the key for which to read the row.
default	object	Specifies a default object containing values for missing columns.
bindings	binding:<{row}>	Specifies the bindings for columns to be bound.
body	any	Specifies the subsequent body statements to be executed.

Return value

The with-default-read is a special form that returns the result of executing the provided body statements.

Examples

The following example demonstrates how to use the with-default-read function to read a row from the accounts table for the specified key, using default values if the row is not found, and binds the balance and currency columns for further processing:

(with-default-read accounts id { "balance": 0, "currency": "USD" } { "balance":= bal, "currency":= currency }
  (format "Balance for {} is {} {}" [id bal currency]))

This example illustrates reading the accounts table with the row key of id and setting default values of 0 and USD for the balance and currency columns if the row isn't found to format a default message using the format function.