预备陈述是否以这种方式工作？

Question

I am trying to populate one table in my database with pretty complex data. For this, I am using a generator API (which gives me random data).

public void populateCrackers(){
    PreparedStatement psm;
    String queryJoke = "(SELECT jid FROM Jokes WHERE jid=?)";
    String queryHat = "(SELECT hid FROM Hats WHERE hid=?)";
    String queryGift = "(SELECT gid FROM Gifts WHERE gid=?)";

    String query = "INSERT INTO Crackers(cid, name, jid, hid, gid, quantity) VALUES(" +
            "?, " +
            "?, " +
            queryJoke + ", " +
            queryHat + ", " +
            queryGift + ", " +
            "?)";

    System.out.println(query);

    String cracker_String = utils.JSONUtils.getJSON(crackerAPI, client);
    JSONObject crackerJSON = new JSONObject(cracker_String);
    JSONArray crackers = crackerJSON.getJSONArray("results");
    for(int j=0; j<crackers.length(); j++){
        try{
            psm = connection.prepareStatement(query);

            psm.setInt(1,crackers.getJSONObject(j).getInt("cid"));
            psm.setString(2, crackers.getJSONObject(j).getString("cname"));
            psm.setInt(3, crackers.getJSONObject(j).getInt("rjoke"));
            psm.setInt(4, crackers.getJSONObject(j).getInt("rhat"));
            psm.setInt(5, crackers.getJSONObject(j).getInt("rgift"));
            psm.setInt(6, crackers.getJSONObject(j).getInt("cquantity"));

            psm.execute();

            System.out.println(crackers.getJSONObject(j).get("cid") + " "
                    + crackers.getJSONObject(j).get("cname") + " "
                    + crackers.getJSONObject(j).get("cquantity") + " "
                    + crackers.getJSONObject(j).get("rjoke") + " "
                    + crackers.getJSONObject(j).get("rhat") + " "
                    + crackers.getJSONObject(j).get("rgift"));


        }catch (Exception e){
            e.printStackTrace();
        }
    }
}

This is the method that populates my "Crackers" tab. I am wondering if this be accepted as a prepared statement. When I run it in psql interactive command line tool, exactly that statement with some chosen ids (eg INSERT INTO Crackers (cid, name, hid, jid, gid, quantity) VALUES('cid', 'name', (SELECT hid FROM Hats WHERE hid=11), (SELECT jid FROM Jokes where jid=99), (SELECT gid FROM Gifts WHERE gid=13), 5) it works flawlessly.

Does my preparedstatement break the Constraint?

Any ideas?

LATER EDIT: The inconsistency is the form of that null values can reach my Crackers table (eg Cracker(1, "hello", null, null, 3, 123) appears in the table.

Answer 1

The code is correct, though the prepared statement must be closed, and it would be better to create the statement once, before the for loop.

Now there is crackers.length() times a statement created but not closed. That might give problems.

Use the try-with-resouce syntax for automatic closing, irrespective of any exception or return.

try (PreparedStatement psm = connection.prepareStatement(query)) {
    for (int j = 0; j < crackers.length(); j++) {
        ...
        psm.executeUpdate();

And call executeUpdate instead of the more general execute . The resulting update count might be of interest (1/0).

Answer 2

There is nothing about Prepared statement. Constraint can be broken by parameters you set to it. And you can run your PLSQL statement as anonimous block in PreparedStatement as well.

Just surround it with BEGIN ... END. only one thing is different - for JDBC parameters are ? mark not :parameter as for PLSQL and there is no way to use named parameter.

That means if you need to use parameter more than once for JDBC you have to have that many ? marks and set all of them.

So, focus on parameters you pass to and their sequence.

Answer 3

I realised I had the wrong constraints on my table. I was letting null values in. There was nothing wrong with the prepared statement.

The right query to create the table is this one:

String createCrackersQuery = "CREATE TABLE Crackers(" +
            "  cid INTEGER," +
            "  name VARCHAR NOT NULL," +
            "  jid INTEGER NOT NULL," +
            "  hid INTEGER NOT NULL," +
            "  gid INTEGER NOT NULL," +
            "  quantity INTEGER NOT NULL," +
            "  CONSTRAINT Cracker_Primary PRIMARY KEY (cid)," +
            "  CONSTRAINT Cracker_Name_Unique UNIQUE(name)," +
            "  CONSTRAINT Joke_Foreign FOREIGN KEY (jid) REFERENCES Jokes(jid)," +
            "  CONSTRAINT Hat_Foreign FOREIGN KEY (hid) REFERENCES Hats(hid), " +
            "  CONSTRAINT Gift_Foreign FOREIGN KEY (gid) REFERENCES Gifts(gid)" +
            ")";