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Editorial Team
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Asked: 2026-05-26T15:42:33+00:00

We’re trying to find out some performance fixes reading from a TADOQuery. Currently, we

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We’re trying to find out some performance fixes reading from a TADOQuery. Currently, we loop through the records using ‘while not Q.eof do begin … Q.next method. For each, we read ID and Value of each record, and add each to a combobox list.

Is there a way to convert all values of a specified field into a list in one shot? Rather than looping through the dataset? It would be really handy if I can do something like…

TStrings(MyList).Assign(Q.ValuesOfField['Val']);

I know that’s not a real command, but that’s the concept I’m looking for. Looking for a fast response and solution (as always but this is to fix a really urgent performance issue).

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  1. Editorial Team

    There are some great performance suggestions made by other folks that you should implement in Delphi. You should consider them. I will focus on ADO.

    You haven’t specified what the back end database server is, so I can’t be too specific, but there are some things that you should know about ADO.

    ADO RecordSet

    In ADO, there is a RecordSet object. That RecordSet object is basically your ResultSet in this case. The interesting thing about iterating through the RecordSet is that it’s still coupled with the provider.

    Cursor Type

    If your cursor type is Dynamic or Delphi’s default Keyset, then each time the RecordSet requests a new row from the provider, the provider will check to see if there were any changes before it returns the record.

    So, for the TADOQuery where all you’re doing is reading the result set to populate the combobox, and it’s not likely to have changed, you should use the Static cursor type to avoid checking for updated records.

    In case you don’t know what a cursor is, when you call a function like Next, you are moving the cursor, which represents the current record.

    Not every provider supports all of the cursor types.

    CacheSize

    Delphi’s and ADO’s default cache size for a RecordSet is 1. That’s 1 record. This works in combination with the cursor type. The cachesize tells the RecordSet how many records to fetch and store at a time.

    When you issue a command like Next (really MoveNext in ADO) with a cache size of 1, the RecordSet only has the current record in memory, so when it fetches that next record, it must request it from the provider again. If the cursor is not Static, that gives the provider the opportunity to get the latest data before returning the next record. So, a size of 1 makes sense for Keyset or Dynamic, because you want the provider to be able to get you the updated data.

    Obviously, with a value of 1, there’s communication between the provider and RecordSet each time move the cursor. Well, that’s overhead that we don’t want if the cursor type is static. So, increasing your cache size will reduce the number of round trips between the RecordSet and the provider. This also increases your memory requirements, but it should be faster.

    Also note that with a cache size greater than 1 for Keyset cursors, if the record that you want is in the cache, it won’t request it from the provider again, which means that you won’t see the updates.

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