Query JSON

D1 has built-in support for querying and parsing JSON data stored within a database. This enables you to:

• Query paths within a stored JSON object - for example, extracting the value of named key or array index directly, which is especially useful with larger JSON objects.
• Insert and/or replace values within an object or array.
• Expand the contents of a JSON object or array into multiple rows - for example, for use as part of a WHERE ... IN predicate.
• Create generated columns that are automatically populated with values from JSON objects you insert.

One of the biggest benefits to parsing JSON within D1 directly is that it can directly reduce the number of round-trips (queries) to your database. It reduces the cases where you have to read a JSON object into your application (1), parse it, and then write it back (2).

This allows you to more precisely query over data and reduce the result set your application needs to additionally parse and filter on.

​​ Types

JSON data is stored as a TEXT column in D1. JSON types follow the same type conversion rules as D1 in general, including:

• A JSON null is treated as a D1 NULL.
• A JSON number is treated as an INTEGER or REAL.
• Booleans are treated as INTEGER values: true as 1 and false as 0.
• Object and array values as TEXT.

​​ Supported functions

The following table outlines the JSON functions built into D1 and example usage.

• The json argument placeholder can be a JSON object, array, string, number or a null value.
• The value argument accepts string literals (only) and treats input as a string, even if it is well-formed JSON. The exception to this rule is when nesting json_* functions: the outer (wrapping) function will interpret the inner (wrapped) functions return value as JSON.
• The path argument accepts path-style traversal syntax - for example, $ to refer to the top-level object/array, $.key1.key2 to refer to a nested object, and $.key[2] to index into an array.

The SQLite JSON extension Open external link , on which D1 builds on, has additional usage examples.

​​ Error Handling

JSON functions will return a malformed JSON error when operating over data that isn’t JSON and/or is not valid JSON. D1 considers valid JSON to be RFC 7159 Open external link conformant.

In the following example, calling json_extract over a string (not valid JSON) will cause the query to return a malformed JSON error:

SELECT json_extract('not valid JSON: just a string', '$')

This will return an error:

ERROR 9015: SQL engine error: query error: Error code 1: SQL error or missing database (malformed
  JSON)`

​​ Generated columns

D1’s support for generated columns allows you to create dynamic columns that are generated based on the values of other columns, including extracted or calculated values of JSON data.

These columns can be queried like any other column, and can have indexes defined on them. If you have JSON data that you frequently query and filter over, creating a generated column and an index can dramatically improve query performance.

For example, to define a column based on a value within a larger JSON object, use the AS keyword combined with a JSON function to generate a typed column:

CREATE TABLE some_table (
    -- other columns omitted
    -- JSON: {"measurement":{"aqi":[21,42,58],"wind_mph":"13","location":"US-NY"}}
    location AS (json_extract(raw_data, '$.measurement.location')) STORED
)

Refer to Generated columns to learn more about how to generate columns.

​​ Example usage

​​ Extract values

There are three ways to extract a value from a JSON object in D1:

• The json_extract() function - for example, json_extract(text_column_containing_json, '$.path.to.value).
• The -> operator, which returns a JSON representation of the value.
• The ->> operator, which returns an SQL representation of the value.

The -> and ->> operators functions both operate similarly to the same operators in PostgreSQL and MySQL/MariaDB.

Given the following JSON object in a column named sensor_reading, you can extract values from it directly.

{
    "measurement": {
        "temp_f": "77.4",
        "aqi": [21, 42, 58],
        "o3": [18, 500],
        "wind_mph": "13",
        "location": "US-NY"
    }
}

-- Extract the temperature value
json_extract(sensor_reading, '$.measurement.temp_f')-- returns "77.4" as TEXT

-- Extract the maximum PM2.5 air quality reading
sensor_reading -> '$.measurement.aqi[3]' -- returns 58 as a JSON number

-- Extract the o3 (ozone) array in full
sensor_reading -\-> '$.measurement.o3' -- returns '[18, 500]' as TEXT

​​ Get the length of an array

You can get the length of a JSON array in two ways:

1. By calling json_array(value) directly
2. By calling json_array(value, path) to specify the path to an array within an object or outer array.

For example, given the following JSON object stored in a column called login_history, you could get a count of the last logins directly:

{
    "user_id": "abc12345",
    "previous_logins": ["2023-03-31T21:07:14-05:00", "2023-03-28T08:21:02-05:00", "2023-03-28T05:52:11-05:00"]
}

json_array(login_history, '$.previous_logins') --> returns 3 as an INTEGER

You can also use json_array as a predicate in a more complex query - for example, WHERE json_array(some_column, '$.path.to.value') >= 5.

​​ Insert a value into an existing object

You can insert a value into an existing JSON object or array using json_insert(). For example, if you have a TEXT column called login_history in a users table containing the following object:

{"history": ["2023-05-13T15:13:02+00:00", "2023-05-14T07:11:22+00:00", "2023-05-15T15:03:51+00:00"]}

To add a new timestamp to the history array within our login_history column, write a query resembling the following:

UPDATE users
SET login_history = json_insert(login_history, '$.history[#]', '2023-05-15T20:33:06+00:00')
WHERE user_id = 'aba0e360-1e04-41b3-91a0-1f2263e1e0fb'

Provide three arguments to json_insert:

1. The name of our column containing the JSON you want to modify.
2. The path to the key within the object to modify.
3. The JSON value to insert. Using [#] tells json_insert to append to the end of your array.

To replace an existing value, use json_replace(), which will overwrite an existing key-value pair if one already exists. To set a value regardless of whether it already exists, use json_set().

​​ Expand arrays for IN queries

Use json_each to expand an array into multiple rows. This can be useful when composing a WHERE column IN (?) query over several values. For example, if you wanted to update a list of users by their integer id, use json_each to return a table with each value as a column called value:

UPDATE users 
SET last_audited = '2023-05-16T11:24:08+00:00'
WHERE id IN (SELECT value FROM json_each('[183183, 13913, 94944]'))

This would extract only the value column from the table returned by json_each, with each row representing the user IDs you passed in as an array.

json_each effectively returns a table with multiple columns, with the most relevant being:

• key - the key (or index).
• value - the literal value of each element parsed by json_each.
• type - the type of the value: one of null, true, false, integer, real, text, array, or object.
• fullkey - the full path to the element: e.g. $[1] for the second element in an array, or $.path.to.key for a nested object.
• path - the top-level path - $ as the path for an element with a fullkey of $[0].

In this example, SELECT * FROM json_each('[183183, 13913, 94944]') would return a table resembling the below:

key|value|type|id|fullkey|path
0|183183|integer|1|$[0]|$
1|13913|integer|2|$[1]|$
2|94944|integer|3|$[2]|$

You can use json_each with D1’s client API in a Worker by creating a statement and using JSON.stringify to pass an array as a bound parameter:

const stmt = context.env.DB
    .prepare("UPDATE users SET last_audited = ? WHERE id IN (SELECT value FROM json_each(?1))")
const resp = await stmt.bind(
    "2023-05-16T11:24:08+00:00",
    JSON.stringify([183183, 13913, 94944])
    ).run()

This would only update rows in your users table where the id matches one of the three provided.