I would like to see only that products user is looking for them, but when second if is executed it will push(pointer or whatever is there) to next ID(id I have as unique so it will push to nowhere) and result is null. I hope you understand my problem :).
if (stmt.execute(
"SELECT * FROM products where ID=" + removeName)) {
rs = stmt.getResultSet();
if (!rs.next()) {
m = "ID not found.";
return m;
}
In your case, you can go for PreparedStatement for avoiding SQL-Injection problem.
PreparedStatement prodsQuery= con.prepareStatement("SELECT * FROM products where ID=?");
prodsQuery.setInt(1,removeName);
ResultSet rs = prodsQuery.executeQuery();
if(!rs.next())
{
m = "ID not found.";
return m;
}
The problem is that you're reading the first result in order to know if there's at least one result, then trying to consume the next results and missing the first one (adapted from your question description). I gave an explanation of how this works here.
A possible solution for this problem would be assuming the query executed with no problems and you have your results, then retrieve the data (or List of data) and as a last step verify if the data is not null or the List of data is not empty.
Code adapted from Naveen's answer to show the proposed solution
PreparedStatement prodsQuery =
con.prepareStatement("SELECT * FROM products where ID=?");
prodsQuery.setInt(1,removeName);
ResultSet rs = prodsQuery.executeQuery();
Assuming there's only one result to get:
//also assuming you will set the results in a Data class (yes, this can be replaced)
Data data = null;
if (rs.next()) {
//logic to retrieve data...
data = new Data();
data.setSomething(rs.get(1));
//more and more code to fill the data...
//because it looks that you need it as String (wonder why you return a String as well)
return data.toString();
}
//note: I use an else statement to check if indeed there were no results at all
//else statement added using a line separator for code explanation purposes
else {
m = "ID not found.";
return m;
}
Assuming there is a list of results to get:
//also assuming you will set the results in a Data class (yes, this can be replaced)
List<Data> dataList = new ArrayList<Data>();
while (rs.next()) {
//logic to retrieve data...
Data data = new Data();
data.setSomething(rs.get(1));
//more and more code to fill the data...
//because it looks that you need it as String (wonder why you return a String as well)
dataList.add(data);
}
//in this case, there's no validation in order to know if there's any result
//the validation must be in the client of this class and method checking if
//the result list is empty using if(!List#isEmpty) { some logic... }
return dataList;
First thing, your approach is vulnerable to SQL Injection. Please go for PreparedStatement.
Look at this simple example for using PreparedStatement
And you should do like this :
ResultSet rs = stmt.executeQuery("SELECT * FROM products where ID=" + removeName);
if (!rs.next()) {
m = "ID not found.";
return m;
}
Related
I created a system in which I can run all my postgre sql queries with only one single Async Task Class in Android Studio. This was really(!!) challenging due to the big amount of limitations that I had to face. But this works actually really great!
//Used for connecting to database and executing queries.
//Index 0 of input string must be the query, Index 1 must be the tablename we demand
//We can only gather data from 1 table for each query, so if you need data from several tablecolumns, use multiple queries like:
//[0] = query, [1] = tablename, [2] = 2nd query, [3] = 2nd tablename, [4] = 3rd query, [5] = 3rd table name ... and so on (each query must come with a tablename)
public class DBHandler extends AsyncTask<String, Void, List<String>>
{
public AsyncResponse delegate;
#Override
protected List<String> doInBackground(String...query)
{
List<String> result = new ArrayList<String>();
String sql;
String tableresult = null;
Connection conn = null;
Statement st = null;
ResultSet rs = null;
try {
Class.forName("org.postgresql.Driver");
conn = DriverManager.getConnection("jdbc:postgresql://192.168.200.300:5439/dbname?user=anonymous&password=secretpw");
st = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE); //necessary if you want to use rs.first() after rs.next(), it makes the resultset scrollable
for (int i = 0; i <= query.length-1; i = i+2) //queries are always stored in i=0 and/or in i+2, because i+1 contain the demanded tablenames for resultset handling
{
System.out.println("I is: " +i);
if (!query[i].isEmpty())
{
System.out.println(query[i]);
sql = query[i];
rs = st.executeQuery(sql);
while (rs.next())
if (!query[i + 1].isEmpty() || !rs.getString(query[i + 1]).isEmpty()) //if i+1 is empty, there is no demanded tablename. Used when we dont need any return values (ie. INSERT, UPDATE)
result.add(rs.getString(query[i + 1])); //demanded tablename is always stored in i+1
//We add an empty entry if we demand multiple tablenames so we can keep them seperate
//Might be replaced with any other char, but you will have to backtrack all usages of DBHandler and fix the filters there
if(i+2 < query.length)
result.add(" ");
}
rs.first(); //reset pointer for rs.next()
}
rs.close();
st.close();
conn.close();
System.out.println("End of AsyncTask");
}
catch (SQLException ex)
{
ex.printStackTrace();
}
catch (Exception e)
{
e.printStackTrace();
}
return result;
}
//onPostExecute returns query result in a List.
//We need to use interaces delegate feature to send the result to other classes, like "Auslieferung", which is implementing the interface
#Override
protected void onPostExecute(List<String> result)
{
super.onPostExecute(result);
System.out.println("Result: " +result.toString());
if (!result.isEmpty())
delegate.processFinish(result);
}
}
There is a for-loop in this Async Task.
for (int i = 0; i <= query.length-1; i = i+2)
And now finally I can explain my issue:
I usually use SELECT queries, sometimes I use an INSERT query (which can be done by a single query), but when I parse an Update Query, my for-loop stops iterating after the first pass, so i+2 never happens. The update queries look like this:
String updatequeries[] = {UPDATE delivery SET contactperson = 'Jon Doe' WHERE officeid = 5, " ", UPDATE delivery SET contactemail = 'abd#def.gh' WHERE officeid = 5, " "};
Why does this for loop stop running right after the first run? The debugger does not show anything unusual, everything was parsed right and there are no queries missing. Updating a table does not return any results, but nothing depends on result values here. I tried to run 20 update queries in a single string var, but the for loop stops after the first iteration anyway. No issues are displayed in the debugger or in the logs. Have I overseen something or is there anything I don't know? Might this be a bug? Please help me! This issue drives me crazy.
I have a problem with my sql query in Java. As you can see below, the query is supposed to return rph_id but it returns only 0, so it only proceeds to the else method.
At first, I did not use prepareStatement but many suggest that I use prepareStatement. But it still won't work. After checking both suggestions, I think my problem is on the query but I don't know what.
public class RphDAO{
static int rph_id;
public static RPHS getRph(RPHS rph) {
try {
currentCon = ConnectionManager.getConnection();
ps=currentCon.prepareStatement("select * from rphs where rph_id=?");
ps.setInt(1, rph_id);
ResultSet rs = ps.executeQuery();
if (rs.next()) {
rs.getInt("rph_id");
rph.setRph_id(rph_id);
rph.setValid(true);
} else {
rph.setValid(false);
}
}
...
return rph;
}
}
It should return an existing id, not 0.
Here:
if (rs.next()) {
rs.getInt("rph_id");
rph.setRph_id(rph_id);
rph.setValid(true);
You get a value from the ResultSet rs ... to then throw that result away.
Probably you meant something like:
rph_id = rs.getInt("rph_id");
On the other hand, your request those entries that have rph_id==1, so I don't see what other value than 1 you expect to find here. Most likely, you want to look into other parts of that result set, and somehow pull those into variables/fields of some object.
It seems as if the OP is simply not familiar with using ResultSet, thus I think the real answer is: go and read a good tutorial on this subject. You can't learn how to use a new API by trial and error. Read its documentation, or a good tutorial that shows you how to use it properly!
I think you should use COUNT instead in your sql since it is no point in setting the id if it is already correct and also use the id from the object given as parameter to the method for consistency.
public static RPHS getRph(RPHS rph) {
try {
currentCon = ConnectionManager.getConnection();
ps=currentCon.prepareStatement("select COUNT(*) from rphs where rph_id=?");
ps.setInt(1, rph.getRph_id);
ResultSet rs = ps.executeQuery();
int count = 0;
if (rs.next()) {
count = rs.getInt(1);
}
rph.setValid(count == 1);
}
So, I'm trying to extract msgID and msgStatus values from database for each reference Id(variable msgRefList) stored in the list object and I'm trying to store these extracted values in String objects for further processing. But rs.next() method is returning false and hence it is not going into the while loop where the assignment statements are. I checked in database with the query that i'm using in the code and it shows one record in the result, but still rs.next() is returning false. Screenshot attached with the database results.
Below is the actual code that i'm using
List<String> msgRefList = listofRefrnceValues:
try {
Connection connect = connectToDB(ENV);
for(String reference: msgRefList){
String query="select ID, MSG_STS from TABLE where INSTR_ID = ?";
PreparedStatement stmt = connect.prepareStatement(query);
stmt.setString(1,reference);
ResultSet rs = stmt.executeQuery();
if(rs!=null){
while(rs.next()) {
P_MID = rs.getString("P_MID");
P_MSG_STS = rs.getString("P_MSG_STS");
}
}
}
}catch (Exception e) {
e.printStackTrace();
}
You have some typos in your SQL-Query-String in java. Instead of TABLE you probably meant MINF (your real table) also all of your properties don't have the prefix P_ and ID is probably MID. So change:
String query="select ID, MSG_STS from TABLE where INSTR_ID = ?";
To:
String query="select P_MID, P_MSG_STS from MINF where P_INSTR_ID = ?";
And you'll be fine.
Im trying to return all the id from authors Table... but isnt working... Just returning me the first ID... But if i delete the return and put to Print, that give me all IDs..
String url = "jdbc:postgresql://localhost/testdb";
String user = "test";
String password = "test*";
try {
con = DriverManager.getConnection(url, user, password);
pst = con.prepareStatement("SELECT id FROM authors");
rs = pst.executeQuery();
while (rs.next()) {
return rs.getInt(1);
}
The return statement by default returns the value of the returned constant/variable, stops the method execution and leave the method. This is explained here: Returning a Value from a Method
To return all the results from the execution of your query, you must store the results in a List and then return this list:
List<Integer> idList = new ArrayList<Integer>();
//accessing to the database and executing the query...
rs = pst.executeQuery();
while (rs.next()) {
//store the ids in the list
idList.add(rs.getInt(1));
}
//close all the resources...
//at the bottom of your method
return idList;
Return play the role of break in this case , i suggest to return ResultSet and iterate over it using for or iterator in the View.
while (rs.next()) {
return rs;
}
And in the view:
while (nameOfYourFunction().next()) {
System.Out.println( rs);
}
return terminates your method call, as it denotes that this is the value, that the method was supposed to compute. Only the first return call in your method will ever get executed. So if you are planning on getting all the results from your query, you should return a collection of all those ids, which you construct before calling return with it.
In order to query the database meta data in Sybase ASE, I found this relevant answer (not the accepted one), to be ideal:
From a Sybase Database, how I can get table description ( field names and types)?
Unfortunately, I can't seem to find any documentation, how I'm supposed to call sp_help from JDBC. According to the documentation, sp_help returns several cursors / result sets. The first one contains information about the table itself, the second one about the columns, etc. When I do this:
PreparedStatement stmt = getConnection().prepareStatement("sp_help 't_language'");
ResultSet rs = stmt.executeQuery();
while (rs.next()) {
System.out.println(rs.getObject(1));
// ...
}
I only get the results from the first cursor. How to access the other ones?
When you have multiple result sets you need to use the execute() method rather than executeQuery().
Here's an example:
CallableStatement cstmt;
ResultSet rs;
int i;
String s;
...
cstmt.execute(); // Call the stored procedure 1
rs = cstmt.getResultSet(); // Get the first result set 2
while (rs.next()) { // Position the cursor 3
i = rs.getInt(1); // Retrieve current result set value
System.out.println("Value from first result set = " + i);
// Print the value
}
cstmt.getMoreResults(); // Point to the second result set 4a
// and close the first result set
rs = cstmt.getResultSet(); // Get the second result set 4b
while (rs.next()) { // Position the cursor 4c
s = rs.getString(1); // Retrieve current result set value
System.out.println("Value from second result set = " + s);
// Print the value
}
rs.close(); // Close the result set
cstmt.close(); // Close the statement
You also need to call getUpdateCount() as well as getMoreResults() to read the entire result set. Here is some code I used to call sp_helpartition to retrieve partition information from a SYBASE DB.
try {
connection = getPooledConnection(poolName);
statement = connection.createStatement();
CallableStatement callable = connection.prepareCall(
"{ call sp_helpartition(?) }");
callable.setString(1,tableName);
callable.execute();
int partitions = 0;
/*
* Loop through results until there are no more result sets or
* or update counts to read. The number of partitions is recorded
* in the number of rows in the second result set.
*/
for (int index = 0 ; ; index ++){
if (callable.getMoreResults()){
ResultSet results = callable.getResultSet();
int count = 0 ;
while (results.next()){
count++;
}
if (index == 1){
partitions = count;
}
} else if (callable.getUpdateCount() == -1){
break ;
}
}
return partitions ;
} catch (Exception e) {
return 0 ;
} finally {
statement.close();
connection.close();
}
Thanks to Martin Clayton's answer here, I could figure out how to query Sybase ASE's sp_help function generically. I documented some more details about how this can be done in my blog here. I worked support for multiple JDBC result sets into jOOQ. In the case of sp_help, calling that function using the jOOQ API might look like this:
Factory create = new ASEFactory(connection);
// Get a list of tables, a list of user types, etc
List<Result<Record>> tables = create.fetchMany("sp_help");
// Get some information about the my_table table, its
// columns, keys, indexes, etc
List<Result<Record>> results = create.fetchMany("sp_help 'my_table'");