How to diagnose and fix the 2203F sql_json_scalar_required error code in Postgres.

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The 2203F error code in PostgreSQL refers to the sql_json_scalar_required error. This error occurs when a JSON scalar value is required but not found. To diagnose and fix this error, you would typically ensure that the JSON data you’re working with contains scalar values where expected and that your queries are correctly formatted to handle JSON data.

Here are some examples and sample code to explain and cover the possibilities:

Example 1: Incorrect JSON Path

If you’re using the jsonb data type and querying for a scalar value with a JSON path that does not point to a scalar, you might encounter this error.

-- Assuming you have a table 'users' with a jsonb column 'data'
-- and you're trying to get a scalar value from a JSON path
SELECT data->'name'->'first' FROM users;

If data->'name'->'first' does not point to a scalar value (e.g., it points to an object or an array), you’ll get the 2203F error.

Fix:

Ensure that the JSON path points to a scalar value.

-- Correct the JSON path to point to a scalar
SELECT data->'name'->>'first' FROM users;

The ->> operator gets the JSON object field as text, ensuring a scalar value is returned.

Example 2: Using JSON Processing Functions Incorrectly

When using functions like jsonb_extract_path_text which expect scalar values, providing a non-scalar JSON element will cause the 2203F error.

-- Assuming 'info' is a jsonb column in 'products' table
SELECT jsonb_extract_path_text(info, 'manufacturer', 'address') FROM products;

If address is an object or an array, not a scalar value, you’ll encounter the error.

Fix:

Make sure to only extract scalar values with these functions.

-- Correct usage to extract a scalar value
SELECT jsonb_extract_path_text(info, 'manufacturer', 'phone') FROM products;

Assuming that phone is a scalar value within the manufacturer object.

Example 3: Using JSON Population Functions on Non-scalars

When populating JSON with functions like jsonb_populate_record or jsonb_to_record, you might encounter the 2203F error if the JSON does not match the expected scalar types of the target record.

-- Assuming you have a type 'user_type' with a 'name' field
SELECT * FROM jsonb_to_record('{"name": {"first": "John", "last": "Doe"}}') 
AS x(name text);

The name is expected to be scalar, but it’s an object.

Fix:

Ensure the JSON structure matches the expected record structure with scalar types.

-- Correct the JSON to provide a scalar for 'name'
SELECT * FROM jsonb_to_record('{"name": "John Doe"}') AS x(name text);

In all cases, diagnosing involves checking the structure of your JSON data and the way you’re querying it to ensure that wherever a scalar value is expected, a scalar value is indeed present. When writing functions or queries that interact with JSON data in PostgreSQL, always ensure that the data types and paths used are appropriate for scalar values when required.

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