MySQL表里有表结构：

CREATE TABLE `json_test`
(
    `id`   bigint NOT NULL AUTO_INCREMENT,
    `data` json DEFAULT NULL,
    PRIMARY KEY (`id`)
) ENGINE = InnoDB
  AUTO_INCREMENT = 1
  DEFAULT CHARSET = utf8mb4
  COLLATE = utf8mb4_0900_ai_ci

表里已有一条数据：

mysql> select * from json_test;
+----+----------+
| id | data     |
+----+----------+
|  1 | {"a": 1} |
+----+----------+
1 rows in set (0.00 sec)

用rbatis的rbdc::Json表示json字段类型，查询可以成功，但是insert失败：

use serde::{Deserialize, Serialize};

#[derive(Clone, Debug, Serialize, Deserialize)]
pub struct JsonTest {
    pub id: u64,
    pub data: rbdc::Json,
}
rbatis::crud!(JsonTest {}, "json_test");

#[cfg(test)]
mod tests {
    use rbatis::RBatis;
    use rbdc::rt::tokio;
    use rbdc_mysql::MysqlDriver;

    use super::*;

    #[tokio::test]
    async fn test_json_field_select() {
        let rb = RBatis::new();
        rb.init(MysqlDriver {}, "mysql://root:123456@localhost:3306/test").unwrap();
        let result = JsonTest::select_by_column(&rb, "id", 1).await;
        // OK
        assert!(result.is_ok());
    }

    #[tokio::test]
    async fn test_json_field_insert() {
        let rb = RBatis::new();
        rb.init(MysqlDriver {}, "mysql://root:123456@localhost:3306/test").unwrap();

        let record = JsonTest {
            id: 2,
            data: rbdc::Json(String::from(r#"{"b":2}"#)),
        };

        // FAILED: called `Result::unwrap()` on an `Err` value: E("1210 (HY000): Incorrect arguments to mysqld_stmt_execute")
        JsonTest::insert(&rb, &record).await.unwrap();
    }
}

如果用String表示json类型字段，插入可以成功，但是查询失败：

use serde::{Deserialize, Serialize};

#[derive(Clone, Debug, Serialize, Deserialize)]
pub struct JsonTest {
    pub id: u64,
    pub data: String,
}
rbatis::crud!(JsonTest {}, "json_test");

#[cfg(test)]
mod tests {
    use rbatis::RBatis;
    use rbdc::rt::tokio;
    use rbdc_mysql::MysqlDriver;

    use super::*;

    #[tokio::test]
    async fn test_json_field_select() {
        let rb = RBatis::new();
        rb.init(MysqlDriver {}, "mysql://root:123456@localhost:3306/test").unwrap();
        let result = JsonTest::select_by_column(&rb, "id", 1).await;
        assert!(!result.is_ok());
        // FAILED: called `Result::unwrap()` on an `Err` value: E("error while decoding value: invalid type: map, expected a string")
        result.unwrap();
    }

    #[tokio::test]
    async fn test_json_field_insert() {
        let rb = RBatis::new();
        rb.init(MysqlDriver {}, "mysql://root:123456@localhost:3306/test").unwrap();

        let record = JsonTest {
            id: 2,
            data: String::from(r#"{"b":2}"#),
        };

        // OK
        JsonTest::insert(&rb, &record).await.unwrap();
    }
}

实在不清楚这个类型的字段该怎么表示了......

用JsonV<T> 结构体，T可以是serde_json::Value 或者任意的json结构体