讲起来有些烦琐。下面是D6DG的文章节选，你读一读吧。 One option for master/detail relationships is nested datasets. Nested datasets allow a master table to actually contain detail datasets. In addition to updating master and detail records in one transaction, they allow for storage of all master and detail records to be stored in one briefcase file, and you can use the enhancements to DBGrid to pop up detail datasets in their own win-dows. A word of caution if you do decide to use nested datasets: All the detail records will be retrieved and brought over to the client when selecting a master record. This will become a possible performance bottleneck if you nest several levels of detail datasets. For example, if you retrieve just one master record that has 10 detail records, and each detail record has three detail records linked to the first level detail, you would retrieve 41 records initially. When using client-side linking, you would only retrieve 14 records initially and obtain the other grandchild records as you scrolled through the detail TClientDataSet . In order to set up a nested dataset relationship, you need to define the master/detail relationship on the application server. This is done using the same technique you’ve been using in client/ server applications—namely, defining the SQL statement for the detail TQuery , including the link parameter. Here’s an example: “select *orders where custno=:custno ” You then assign the TQuery.Datasource for the detail TQuery to point to a TDatasource com-ponent that’s tied to the master TDataset . Once this relationship is set up, you only need to export the TDatasetProvider that’s tied to the master dataset. DataSnap is smart enough to understand that the master dataset has detail datasets linked to it and will therefore send the detail datasets across to the client as a TDatasetField . On the client, you assign the master TClientDataset.ProviderName property to the master provider. Then, you add persistent fields to the TClientDataset . Notice the last field in the Fields Editor. It contains a field named the same as the detail dataset on the server and is declared as a TDatasetField type. At this point, you have enough information to use the nested dataset in code. However, to make things really easy, you can add a detail TClientDataset and assign its DatasetField property to the appropriate TDatasetField from the master. It’s important to note here that you didn’t set any other properties on the detail TClientDataset , such as RemoteServer , ProviderName , MasterSource , MasterFields ,or PacketRecords . The only property you set was the DatasetField property. At this point, you can bind data-aware controls to the detail TClientDataset as well. After you’ve finished working with the data in the nested dataset, you need to apply the updates back to the database. This is done by calling the master TClientDataset ’s ApplyUpdates()method. DataSnap will apply all the changes in the master TClientDataset , which includes the detail datasets, back to the server inside the context of one transaction. You ’ll find an example on the book’s CD-ROM in the directory for this chapter under \NestCDS .
自己up
One option for master/detail relationships is nested datasets. Nested datasets allow a master
table to actually contain detail datasets. In addition to updating master and detail records in one
transaction, they allow for storage of all master and detail records to be stored in one briefcase
file, and you can use the enhancements to DBGrid to pop up detail datasets in their own win-dows.
A word of caution if you do decide to use nested datasets: All the detail records will be
retrieved and brought over to the client when selecting a master record. This will become a
possible performance bottleneck if you nest several levels of detail datasets. For example, if
you retrieve just one master record that has 10 detail records, and each detail record has three
detail records linked to the first level detail, you would retrieve 41 records initially. When
using client-side linking, you would only retrieve 14 records initially and obtain the other
grandchild records as you scrolled through the detail TClientDataSet .
In order to set up a nested dataset relationship, you need to define the master/detail relationship
on the application server. This is done using the same technique you’ve been using in client/
server applications—namely, defining the SQL statement for the detail TQuery , including the
link parameter. Here’s an example:
“select *orders where custno=:custno ”
You then assign the TQuery.Datasource for the detail TQuery to point to a TDatasource com-ponent
that’s tied to the master TDataset . Once this relationship is set up, you only need to
export the TDatasetProvider that’s tied to the master dataset. DataSnap is smart enough
to understand that the master dataset has detail datasets linked to it and will therefore send the
detail datasets across to the client as a TDatasetField .
On the client, you assign the master TClientDataset.ProviderName property to the master
provider. Then, you add persistent fields to the TClientDataset . Notice the last field in the
Fields Editor. It contains a field named the same as the detail dataset on the server and is
declared as a TDatasetField type. At this point, you have enough information to use the
nested dataset in code. However, to make things really easy, you can add a detail
TClientDataset and assign its DatasetField property to the appropriate TDatasetField
from the master. It’s important to note here that you didn’t set any other properties on the detail
TClientDataset , such as RemoteServer , ProviderName , MasterSource , MasterFields ,or
PacketRecords . The only property you set was the DatasetField property. At this point, you
can bind data-aware controls to the detail TClientDataset as well.
After you’ve finished working with the data in the nested dataset, you need to apply the
updates back to the database. This is done by calling the master TClientDataset ’s
ApplyUpdates()method. DataSnap will apply all the changes in the master TClientDataset ,
which includes the detail datasets, back to the server inside the context of one transaction.
You ’ll find an example on the book’s CD-ROM in the directory for this chapter under
\NestCDS .
a1 where.....'
具体的代码明天给你
在客户端 datasource 的onchange 事件中
var
label1:tlabel;
begin
label1:=tlabel.creat(form1);
try
label1.parent:=form1;
clientdataset1.open;
label1.caption:=clientdataset1.filds[0].asstring;
clientdataset2.close;
clientdataset2.commandtext:='select*from b where a="'+label1.caption+'"'';
clientdataset1.open;
finally
label1.free;
end;