Outset: I am building a page in JSP / EJB (Java EE 8) that displays 2 tables: 1 for every user registerd in the database with their name and score and another one that displays all pending challenges to rock-paper-scisors for the currently logged in user.
Databases: So far I have 2 tables in that can be access via the " LOCALHOST. " prefix: Usercredentials and Pending_Challenges. Both were created using the following code:
Database: JavaDB
Usercredentials:
CREATE TABLE USERCREDENTIALS (
username varchar(10) primary key,
password varchar(10) not null
);
Yes, yes I know these are not the best fields to use but I blame my team mate! :)
Pending_Challenges:
CREATE TABLE PENDING_CHALLENGES (
challenge_id integer primary key,
from_user varchar(10) references Usercredentials(username),
to_user varchar(10) references Usercredentials(username),
);
The tables hold the following data so far:
Username | Password | Score
---------------------------
tom | tom | 5
mo | mo | 2
jon | jon | 0
Challenge_ID | From_User | To_User
----------------------------------
1 | tom | mo
2 | jon | tom
I call on these tables in a file named ListUserServlet.java where I run 2 queries. Each one is to create a different set of results (code below ofc) to be printed in 2 different tables.
{... working Java code...}
System.out.println("Creating EMF query for userList");
String query = "SELECT U FROM Usercredentials U ORDER BY U.score DESC";
List users = em.createQuery(query).getResultList();
request.setAttribute("userList", users");
{... working Java code...}
In my .jsp file that then displays the table, I get the following (don't mind the ID tags, we're changing that):
<h3>Current rankings:</h3>
<form id="challengeUserForm" action="ChallengeUser" method="POST">
<table id="userListTable" border="3">
<tr >
<th>Username</th>
<th>Challenge others</th>
<th>Score</th>
</tr>
<c:forEach var="user" begin="0" items="${requestScope.userList}">
<tr>
<td>${user.username} </td>
<td><input type="submit" id="${user.username}" value="Challenge!"></td>
<td>${user.score}</td>
</tr>
</c:forEach>
</table>
Using this approach, I also managed to print out ALL of the currently held challenges in that table by using:
{... working Java code...}
query = "SELECT P FROM PendingChallenges P";
List chall = em.createQuery(query).getResultList();
request.setAttribute("pendingList", chall);
{... working Java code...}
Now, using the same logic, this is how I print the table:
<h3>Pending challenges:</h3>
<form id="acceptChallengeForm" action="AcceptChallenge" method="POST">
<table id="pendingTable" border="3">
<tr>
<th>Username</th>
<th>Accept challenge</th>
</tr>
<c:forEach var="pending" begin="0" items="${requestScope.pendingList}">
<tr>
<td>${pending.fromUser.username} </td>
<td><input type="submit" id="${pending.fromUser.username} " value="Accept!"></td>
</tr>
</c:forEach>
</table>
</form>
I need to get every row from column "from_user" that is NOT the currently logged in user (session variable is in place already). My simple thinking was to include a "NOT LIKE" statement in the Pending query:
query = "SELECT P.fromUser FROM PendingChallenges P WHERE P.fromUser NOT LIKE '" + current_user + "'";
"current_user" is that EJB session String I mentioned.
However, every time I run it, I either get errors saying that either "P.fromUser" is not a String, "P.fromUser.username" does not belong to "entity[Usercredentials]" or the like OR the keyword "LIKE" has not been recognised -> Something along the lines of SQLException Error Code 30000.
I would read about "SQL joins".
The query should be something like this to get the fields from the user credentials table:
SELECT * FROM PendingChallenges P
INNER JOIN UserCredentials U ON P.fromUser = U.username
WHERE P.fromUser != '" + current_user + "'"
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