问题
I have been using DBExpress connections to various databases (mostly MSSQL, Sybase SQL) with:
SQLConnection -> SQLDataSet -> DataSetProvider -> ClientDataSet.
I need to connect to the databases in a fashion that does NOT write changes back to the tables.
So, the DataSetProvider has ResolveToDataSet:=false, and the ClientDataSet has LogChanges:=false (for performance).
In use I connect the SQLConnection, open the ClientDataSet, and then close the SQLConnection.
I can then manipulate the ClientDataSet without fear of changing the underlying table.
I'm new to FireDAC (XE8), and I'm looking to establish the same sort of scenario - load data into memory from a SQL query, and safely manipulate this data in memory without accidentally updating the source table(s).
I'm currently using: FDConnection -> FDQuery and a FDMemTable
The FDQuery has CachedUpdates := true and I perform:
FDQ.Open;
FDQ.FetchAll;
FDMemT.CloneCursor(FDQ,true,false);
FDQ.Close;
I think this is pretty much equivalent - I end up with the data in an FDMemTable such that editing the data will not be able to "write back" to tables.
One other issue - in the dbExpress scenario, I often add InternalCalc Fields to the ClientDataSet. It isn't clear to me that I can do that (and have persistent field names) if I'm performing a CloneCursor operation.
Is there a simpler way of ensuring the data never updates the database? Setting the FDQuery to read-only doesn't work - I often have to modify records (but do not wish to persist these changes).
TIA.
EdB
回答1:
There is a much easier way. Use the FDMemTable's CopyDataSet method. This will copy both the data and the metadata. Changes to the FDMemTable will not be written to the underlying dataset, and internal calc fields (and calculated field) will be copied as well, though you'll have to wire up the OnCalcFields event handler.
FDMemTable1.CopyDataSet( FDQuery1, [coStructure, coRestart, coAppend]);
来源：https://stackoverflow.com/questions/33354428/firedac-equivalent-of-dbexpress-briefcase-model