Say I have a query like the one below. What would be the best way to put each value into an array if I don't know how many results there will be? Normally I would do this with a loop, but I have no idea how many results there are. Would I need run another query to count the results first?
<CFQUERY name="alllocations" DATASOURCE="#DS#">
SELECT locationID
FROM tblProjectLocations
WHERE projectID = '#ProjectName#'
</CFQUERY>
Depending on what you want to do with the array, you can just refer to the column directly for most array operations, eg:
i = arrayLen(alllocations["locationID"]);
Using that notation will work for most array operations.
Note that this doesn't "create an array", it's simply a matter that a query columns - a coldfusion.sql.QueryColumn object is close enough to a CFML array for CF to be able to convert it to one when an array is needed. Hence the column can be passed to an array function.
What one cannot do is this:
myArray = q["locationID"];
This is because by default CF will treat q["locationID"] as a string if it can, and the string value is what's in the first row of the locationID column in the q query. It's only when an array is actually required will CF convert it to an array instead. This is basically how loose-typing works.
So if you just need to pass your query column to some function that expects an array, you can use the syntax above. If you want to actually put the column into a variable, then you will need to do something like this:
myArray = listToArray(valueList(q.localtionID));
NB: make sure you use <cfqueryparam> on your filter values instead of hard-coding them into your SQL statement.
myquery.column.toArray() is also a good undocumented choice.
Since you're only retrieving 1 field value from the query, you could use ValueList() to convert the query results into a comma-delimited list of locationIds, then use listToArray() to change that list into an array.
If you were retrieving multiple field values from the query, then you'd want to loop through the query, copy all the field values from the given row into a struct, and then add that struct to an array using arrayAppend().
(If you're not familiar with these functions, you can look them up in the Adobe docs or on cfquickdocs.com).
Related
A coldfusion query's column can be referenced like a 2D array from what I know of my past experience. Sometimes though I get this issue.
create query from spreadsheet
put column names into an array
only get first element when trying to access the row
have to use a workaround
//imports is a query object after this function
var imports = convertSpreadsheetWOHeaders(spreadsheet, 1);
//this is used to give name values in the json struct, not to access the query columns
var jsonHeaders = ListToArray("number,constructiontype,description,site_address,parcel,permit_date,note_Applicant,note_Contractor,valuation,note_Bld_Fees,note_Other_Fees");
//this gives me ["col_1","col_2","col_3",,,etc]. used to access query columns
var columnHeaders = imports.getColumnNames();
writeDump(imports[columnHeaders[1]]);
writeDump(imports);
I am left with just the first element in column one. And I get of course:
Message: You have attempted to dereference a scalar variable of type class java.lang.String as a structure with members.
When trying to do this:
structInsert(jsonStruct,jsonHeaders[j],imports[columnHeaders[j]][i]);
However, this works:
writeDump(ListToArray(ArrayToList(imports[columnHeaders[1]],'|'),'|',true));
I first do a dump of imports["col_1"] and i get only the first element.
Then I do a dump of ListToArray(ArrayToList(imports["col_1"])) like you see in the above image and it gives me the whole column.
Why can I not access the column correctly in the first place?
The Real Problem:
I was originally trying to access the jsonHeaders list as an array without doing ListToArray() on it. After that my function worked.
BUT. This next part is helpful.
When attempting to access a query object, doing queryObject["columnName"] is considered a shortcut of queryObject["columnName"][1] so coldfusion will just give you the first element.
But when I said ListToArray(ArrayToList()) coldfusion sees that ArrayToList MUST take in an array so an exception is made and the column is returned as an array.
To get a column back as an array to work with you can do a couple things
ListToArray(ArrayToList(query["column"]));
ListToArray(valueList(query.column));
valueArray(query, "column");
Is there an API call provided by mysql++ to get the number of rows returned by the result?
I have code structured as follows:
// ...
Query q = conn.query(queryString);
if(mysqlpp::UseQueryResult res = query.use()){
// some code
while(mysqlpp::Row row = res.fetch_row()){
}
}
My previous question here will be solved easily if a function that returns the number of rows of the result. I can use it to allocate memory of that size and fill in as I iterate row by row.
In case anyone runs into this:
I quote the user manual:
The most direct way to retrieve a result set is to use Query::store(). This returns a StoreQueryResult object,
which derives from std::vector, making it a random-access container of Rows. In turn,
each Row object is like a std::vector of String objects, one for each field in the result set. Therefore, you can
treat StoreQueryResult as a two-dimensional array: you can get the 5th field on the 2nd row by simply saying
result[1][4]. You can also access row elements by field name, like this: result[2]["price"].
AND
A less direct way of working with query results is to use Query::use(), which returns a UseQueryResult object.
This class acts like an STL input iterator rather than a std::vector: you walk through your result set processing
one row at a time, always going forward. You can’t seek around in the result set, and you can’t know how many
results are in the set until you find the end. In payment for that inconvenience, you get better memory efficiency,
because the entire result set doesn’t need to be stored in RAM. This is very useful when you need large result sets.
A suggestion found here: http://lists.mysql.com/plusplus/9047
is to use the COUNT(*) query and fetch that result and then use Query.use again. To avoid inconsistent count, one can wrap the two queries in one transaction as follows:
START TRANSACTION;
BEGIN;
SELECT COUNT(*) FROM myTable;
SELECT * FROM myTable;
COMMIT;
I'm attempting the use QuerySetCell to change value of a specific column in a query object, and have been receiving this error:
Column names must be valid variable names. They must start with a letter and can only include letters, numbers, and underscores.
The reason for this error, and the complication here, is that the columns I am trying to update have some integers as names, taken from a separate record's key/ID. For example, the query may contain three columns with names: "6638, 6639, 6640".
Now, I understand why this error is occurring (though not necessarily why CF has this limitation), however cannot come up with a work around. The further complications are that I cannot make any changes as to how the initial query set's column names, and need to preserve the column names and their order for when I convert the query to a JSON string and update my results table using the JSONified query.
Has anyone encountered this issue before, and if so how were you able to work around it, or were you forced to change how the columns were named in your initial query?
Using CF8 and have the ability to edit the JSONified query after it is returned from my Ajax handler if that makes a difference.
You can use bracket notation to set the values in a query (at least you can in CF9 - I do not have CF8 installed to test).
The sytax is pretty simple:
<cfset queryName[columnName][row] = "some new value" />
From your example, you could use this:
<cfset myQuery["6638"][1] = "moo" />
This will set the value of the '6638' column in the first row to 'moo'. If you have multiple rows being returned, you would need to set each row.
I'm trying to use SQL like select column from table where column in (?)
as ? should be concatenation of strings. I did script, that concatenates rows in something like 'string','secondstring' and so on.
I know, I should use just more parameters, but to the moment of execution I don't know, how many arguments there will be, and that is hundreds of them each time.
I'd like to do it in one SQL, so putting every argument in a single row, and check "execute for each row" isn't perfect either.
Any clue, how to do this?
You can use the cycles and variables kettle.
For example:
-create a job that contains:
1)a transformation where you store in an environment variable
(setVariable ("varname" value, "r") r is the parameter to be accessible by the parent job) the concat all input rows.
2)a transformation which makes the desired query with variable replacement (SELECT column FROM table WHERE column IN (${varname})).
If you need I can send the example files.
Using oracle OCCI is it possible instead of supplying an index for the column when requesting data from a query resultset, to actually pass the column name and get the data?
So instead of doing: (pseudocode)
std::string query = "SELECT NAME FROM CUSTOMERS;";
std::string myresult = oracle.getString(1); // name column in query
you'd do this:
std::string myresult = oracle.getString("NAME"); //column name to get string from
is there any way to do this? I have looked around, but been unable to find anything, besides perhaps going to fetch the table's metadata.
I just read the documentation.
It says ResultSet has a method getColumnListMetaData(), which produces a vector of MetaData.
Most probably you can then use MetaData::getString to find the name of column.
And if so then you can use a std::map<string, int> to map the column names back to indices.
And with that name → index mapping in place you can then implement a getString that takes a query result and column name as arguments.
Possibly someone who has used this particular database can help you better, but it seems that all that was needed was to take a look at the documentation.
Cheers & hth.,