In all of my Delphi programs - until recently - all the DBGrids have been read only: the data displayed is retrieved by a query, and if I want to edit any of the data, a separate 'edit' dialog box is opened with the row's data displayed. This is something that I have been doing ever since I was introduced to Delphi over 20 years ago and there are (at least) two reasons for doing so. The first is that almost all of the queries that are displayed are not 'live queries' (I think that's the term) as the data displayed comes from more than one table. The second reason is that many of the fields display data that come from lookup tables.
That's probably not very clear, so I'll use the example on which I was working today: a list of contact people for a given customer. The query itself involves two tables: contacts and a junction table between the contacts and customers (a contact person can be connected to more than one customer; a customer can have more than one contact). Such a query by default is not 'live'. I could have had a field that defines the type of contact, e.g. one who deals with the financial side, one who receives reports, etc, where these values would be in another table. As it happens, one contact can have more than one role, so there is no type field; instead there are several flags indicating whether the contact is financial, receives reports, etc.
Those flag fields are now editable in situ within the grid; one doesn't have to execute the separate 'edit' dialog box in order to change their value. How did I do this?
- The grid now has the dgEditing flag set in its options property.
- On the grid, I right clicked, entered the 'columns editor' and added all the columns. These come from the query that is linked to the grid so there's no need to add them manually.
- All of the columns were marked as read-only = true; some of them were marked as visible = false.
- The fields that I wanted to be editable were marked as read-only = false.
I naively thought that I need do no more, but there was one more critical step that needed to be taken (ironically, I had done this in the blog manager program a few weeks ago, but there I didn't know about the grid's columns editor, so all the fields are editable; I trust myself only to edit one field). I added an 'update' query that updates the flags' value in the underlying table (contact2cust); this query is executed in the datasource's OnUpdateData method. Doing so turns the temporary change (stored in the clientdataset) into a permanent one (stored in the database). Funnily enough, I had a similar situation in Priority a few days ago: a change would be visible but would not be saved.
The flags are shown as checkboxes drawn on the grid, but when they are edited, their real nature is disclosed - they have one of the values 0 or 1. The user has to enter the appropriate value in order to change the state of the checkbox. Of course, this wouldn't be a problem if a normal text or integer field were involved.
A challenge for myself: how to allow editing a field in situ when the value has to come from a lookup table. I remember seeing a long time ago code that allows one to draw a combobox in a grid, so that will be the starting point. I don't have any need for this at the moment so I'm not going to devote any time to this.
| Title | Tags | ||
|---|---|---|---|
| 564 | Lost videocassettes reappear | TV series | |
| 1017 | Thesis update | DBA | |
| 1488 | Cystoscopy | Health | |
| 1596 | The end of the country as we knew it | Israel |
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