Enforce that a record exists when adding a table reference

Hi there! In this guide, we'll walk through how to ensure that when you're adding a new record to a table, the reference you're providing actually exists in the referenced table. This is a crucial step to maintain data integrity and prevent errors in your application.

Step 1: Identify the Reference Field

First, let's identify the field in your table that references another table. In our example, we have a "Deal" table that includes a "merchant_id" field, which references the "Merchant" table.

Step 2: Get the Referenced Record

Before adding a new record, we need to fetch the referenced record from the other table to ensure it exists. In Xano, you can use the "Get Record" function for this purpose.

1. Drag the "Get Record" function onto the workflow canvas.
2. Set the "Table" to the table you're referencing (in our case, "Merchant").
3. Set the "Field Name" to the field you're looking up (in our case, "id").
4. Set the "Value" to the input value you're receiving (in our case, "merchant_id").
5. Give the output a descriptive variable name (we'll call it "merchant").

Step 3: Add a Precondition

Preconditions in Xano allow you to define a condition that must be true before proceeding with the next step. If the condition is false, you can specify a custom error message.

1. Drag the "Precondition" function onto the workflow canvas, placing it after the "Get Record" function.
2. Set the condition to check if the "merchant" variable (the output of the "Get Record" function) is not equal to null.
3. Provide a custom error message to display if the condition is false (e.g., "This is not a valid merchant").

Step 4: Add the New Record

If the precondition passes (i.e., the referenced record exists), you can proceed to add the new record as usual.

1. Drag the "Add Record" function onto the workflow canvas, placing it after the "Precondition" function.
2. Set the "Table" to the table you're adding the record to (in our case, "Deal").
3. Map the input values to the respective fields in the table.

And that's it! Now, when you try to add a new "Deal" record with an invalid "merchant_id" (i.e., a merchant that doesn't exist in the "Merchant" table), Xano will display the custom error message you specified in the precondition.

By following these steps, you can ensure that your API enforces table references, maintaining data integrity and preventing errors caused by invalid references. This not only improves the reliability of your application but also provides a better user experience by catching and handling such issues proactively.