如何在 java 中为 mysql 的 JSON 数据类型使用准备好的语句？

Question

I have a JSON column that I want to create a prepared statement for, but I'm not sure how to go about it since the parameters for the statement are inside a literal string.

For example:

PreparedStatement stmt = myConn.prepareStatement("SELECT JSON_SET(new_friends, '$.?', '[?]') from friend_list where id = ?");

for (int i = 0; i < new_friends.size(); i++) {
        String friend = new_friends.get(i);

        // not sure what to put here
        stmt.set....
        stmt.set....
        stmt.set(3, i);
}

Anyone have any suggestions?

Answer 1

? placeholders are not used like string interpolation. They replace entire parameters. When the function argument is a string, the entire argument must be the literal string or built with SQL string functions taking parameters as further arguments.

Assuming your syntax is correct for what you want to achieve, consider these:

JSON_SET(new_friends, '$.?', '[?]') -- not valid
JSON_SET(new_friends, ?, ?) -- valid
JSON_SET(new_friends, CONCAT('$.',?), CONCAT('[',?,']')) -- valid

Parameter 1 would be set to the string $.foo for a query in the style of line 2 above, or foo in the style of line 3.

The reason your version isn't valid is exactly the reason you don't/can't use something like WHERE username = '?' but instead would use WHERE username = ? (no quotes around ? ).

Answer 2

If you want to add java list objects into a json array like mentioned below:

{"abc":["var1":"val1","var2":"val2","var3":"val3"]}

If there is already a json value in the column then you can use JSON_SET to update value.

            String query;
            query = "UPADTE tbl1 SET col1 = JSON_SET(col1, '$.abc', CAST(? AS JSON) ) WHERE cdtn = ?"; 
            // if col1 is null then, JSON_SET would be: JSON_SET('{}', '$.abc', CAST(? AS JSON) )
            try (Connection conn = DBUtil.getConnection();
                 PreparedStatement ps = conn.prepareStatement(query)) {
                ps.setString(1, jsonArray.toString());
                ps.setString(2, cd);
                ps.executeUpdate();
            }
            catch (SQLException e) {
                log.error("Error : ", e);
            }