Overview
The Module Dataset is composed by the The Datasets Data Server Service that will receive the request from the various modules, access the data sources, and reply to the requests.
In order to fully leverage the Module Datasets is important to understating various advanced aspects such as: managing parallel requisitions, doing synchronous or asynchronous requests, mapping data to tags in the server side or in the client side the application, performance and others items.
If you are new user, or in simple projects, it's not necessary to review all those concepts up front, before using the Dataset Module. But, if you are deploying projects in production that required exchange of data with SQL database is recommended the you review those topics and how they may apply to specific solution architecture.
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Execution Process
The Dataset module, specifically the "TRunModule.exe (Dataset)" process, reads all project configurations relevant to this module but does not directly interface with the databases. Database access services are provided by TServer, with the Dataset module consuming these services.
Connections with the Database
For each configured database (DB), there's only one access connection. This signifies a single execution thread per DB. However, for parallel execution of commands to the same database, additional DBs can be configured, all pointing to the same database.
Synchronous and Asynchronous Methods in Tables and Queries
The properties in Tables and Queries can trigger execution, such as triggering the "Select" property, which makes the execution asynchronous. This means that after the trigger in the property, the execution continues normally. In parallel, this property propagates from its trigger source (screen or script) to the server, then synchronizes with the Dataset module. The module then makes necessary calls to TServer's bank access service. After TServer's return with the Select execution for the Dataset module, the result gets updated in the module's properties and attributes, is processed for tag mapping, and is finally made available to the entire project.
Contrarily, available methods execute synchronously. For instance, calling the SelectCommand method locks the execution at this method while the Dataset module executes the call of the TServer service, interfaces with the database, and returns the result to the Dataset module. The Dataset module then processes the tag mapping and provides the result in the form of the method's return, allowing the continuation of the execution.
Special caution is required with synchronous calls within code-behind screens (mono-thread, WPF or HTML5 screens). Mechanisms like using Script task or Action Server Request can help create an asynchronous execution without needing to use attributes, when there's a need to handle the result even after an asynchronous execution.
Usage of Client-Type Tags in the Dataset Module's Tag Mapping
Client-type tags can be used in the Dataset module's tag mapping. During execution of a synchronous or asynchronous command, the assignment in the tags gets executed by the Dataset module (not by TServer) in the original domain of the call. Hence, if the call was executed on a client (screen or client script), after the result's return from TServer to the Dataset module, the mapping between received values and tags gets executed. Client domain Tags can be used in the mapping, which allows for specific control over the scope of availability of the value - either for the entire project (using server domain tags) or just for the client's scope (using client domain tags).
Attributes and Server Domain Properties (Concurrency Management)
All module attributes are server domain. Therefore, if multiple Tasks or clients are using the same attributes, there might be competition and confusion in execution. For example, if a client and a Task both set the SQLStatement of a query simultaneously with different values, the last value in the SQLStatement will be used in the operation.
Use of Tag DataTable
The return of Select methods is a .Net DataTable object. This can be manipulated directly in the script or assigned to a Tag of the DataTable type, allowing the result to propagate to other modules like clients or reports.
Dataset Module Properties
There are several server domain properties within the Dataset module, including a .Net DataTable type property called AsyncContents. When the Select property is triggered, initiating an asynchronous execution, the column values of the first row are assigned to the tags configured in the Mapping
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