regression: JSON columns can not be parsed into String anymore since 0.8

[ilka-schulz]

Bug Description

If have a table with one column having the JSON type (internally defined as LONGTEXT by MariaDB). I used to be able to decode this with query_as into a String. Roughly since version 0.8 this panics:

error occurred while decoding column 1: mismatched types; Rust type alloc::string::String (as SQL type VARCHAR) is not compatible with SQL type BLOB

Minimal Reproduction

CREATE TABLE IF NOT EXISTS my_table (
    name VARCHAR(64) PRIMARY KEY,
    json_definition JSON
    CHECK (JSON_VALID(json_definition))
);
INSERT INTO my_table (name, json_definition) VALUES ("foo", "{\"bar\":true}");

/*
let POOL = MySqlPoolOptions::new()
                .max_connections(100)
                .acquire_timeout(Duration::from_secs(30))
                .idle_timeout(Duration::from_secs(10))
                .connect_with({
                    let options = MySqlConnectOptions::new()
                        .host(CONFIG.get().unwrap().db_host.as_str())
                        .username("api")
                        .password(CONFIG.get().unwrap().db_password.as_str())
                        .charset("utf8mb4")
                        .database("warehouse")
                        .log_statements(LevelFilter::Debug)
                        .log_slow_statements(
                            LevelFilter::Warn,
                            std::time::Duration::from_millis(1000),
                        );
                    options
                })
                .await
                .unwrap();
*/
let row: Option<(String, String)> =
    sqlx::query_as("SELECT name, json_definition FROM my_table WHERE name=?")
        .bind("foo")
        .fetch_optional(POOL)
        .await
        unwrap();

Info

• SQLx version: 0.8.2 (it works fine on sqlx 0.7.4)
• SQLx features enabled: [ "runtime-tokio-rustls" , "mysql", "chrono" ]
• Database server and version: MariaDB 10.11.6
• Operating system: Debian 11
• rustc --version: rustc 1.85.0-nightly (4d669fb34 2024-12-08)

[abonander]

Likely caused by #3387.