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Data Controls & Data Binding

This document describes how the Vybe runtime handles database access and data binding, mimicking both legacy VB6 (ADODB) and modern .NET (ADO.NET) APIs.

Architecture Overview

The data access system follows a multi-layered approach:

1. VB Expression Layer: The Interpreter parses and evaluates VB commands (e.g., rs.MoveNext(), adapter.Fill(ds)).
2. Object Proxy Layer: Runtime objects (DbConnection, DbRecordset, etc.) are represented as ObjectData with internal fields like __type and __rs_id.
3. Internal API (interpreter.rs): Logic that translates VB method calls into Data Access Manager calls and handles lazy loading/binding.
4. Data Access Manager (data_access.rs): A global manager that drives sqlx to interact with SQLite, PostgreSQL, and MySQL.

Database Components

Supported Providers

Vybe maps various legacy provider strings to modern backends:

• SQLite: Data Source=mydb.db, Provider=Microsoft.Jet.OLEDB.4.0 (mapped for compatibility).
• PostgreSQL: Host=...;Database=..., Provider=PostgreSql.
• MySQL: Server=...;Database=..., Provider=SQLOLEDB (shared mapping).

Component Instantiation

Components are instantiated by the Interpreter when it encounters a New expression.

VB Class Name	Internal __type	Purpose
ADODB.Connection / SqlConnection	DbConnection	Manages database sessions.
ADODB.Command / SqlCommand	DbCommand	Represents a SQL statement or stored procedure.
ADODB.Recordset	DbRecordset	VB6-style forward/backward-navigable results.
SqlDataReader / OleDbDataReader	DbReader	.NET-style forward-only stream of results.
SqlDataAdapter / OleDbDataAdapter	DataAdapter	Bridge between database and DataSet/DataTable.
System.Data.DataTable	DataTable	In-memory table of data.
System.Data.DataSet	DataSet	In-memory cache of multiple tables.

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Core Database Methods

DbConnection

• Open(): Establishes the connection using ConnectionString.
• Close(): Tears down the connection and resource pool.
• Execute(sql): Directly executes a command; returns a Recordset for SELECTs or rows affected for non-queries.
• BeginTransaction(): Starts a database transaction.

DbCommand

• ExecuteReader(): Executes the CommandText and returns a DbReader.
• ExecuteNonQuery(): Executes the command and returns the number of affected rows.
• ExecuteScalar(): Executes the command and returns the first column of the first row.
• Parameters.AddWithValue(name, value): Adds a parameter for sanitized SQL execution.

DbRecordset (VB6 Style)

• Open(sql, conn): Executes a query on a connection.
• MoveNext(), MovePrevious(), MoveFirst(), MoveLast(): Navigates the cursor.
• EOF, BOF: Flags for end/beginning of file.
• Fields(name).Value: Accesses column data.

DbReader (.NET Style)

• Read(): Advances to the next row; returns True if successful.
• GetValue(index), GetString(index): Accesses typed column data.
• IsDBNull(index): Checks for null values.

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Data Binding System

Vybe provides a sophisticated data binding layer that synchronizes the runtime state with the UI frontend.

BindingSource

The BindingSource is the primary orchestrator for UI synchronization.

• Positioning: Automatically handles MoveNext, MovePrevious, etc., and notifies the UI.
• Lazy Loading: If a BindingSource is linked to a DataAdapter that hasn't been filled, it triggers an auto_fill_data_adapter call.
• Synchronization: When the Position or DataSource changes, it pushes BindingPositionChanged or DataSourceChanged side effects to the frontend.

DataBindings Collection

Every WinForms control in Vybe has a DataBindings collection.

• Add(property, dataSource, dataMember): Establishes a link (e.g., TextBox.Text bound to BindingSource.CustomerName).
• Update Mechanism: When the BindingSource moves to a new row, refresh_bindings is called, which pushes PropertyChange side effects for every bound property.

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Technical Details

Lazy Loading (auto_fill_data_adapter)

To simplify development, Vybe can automatically fill data adapters. If a BindingSource attempts to access data from an unfilled DataAdapter, the runtime:

1. Resolves the ConnectionString.
2. Opens a temporary connection if needed.
3. Executes the SelectCommand.
4. Stores the resulting __rs_id on the adapter.

UI Synchronization via Side Effects

The runtime communicates with the frontend using a side_effects queue:

• DataSourceChanged: Sent when a DataGridView or BindingSource gets a new data source. Includes all columns and rows for immediate rendering.
• PropertyChange: Sent when a bound value changes (e.g., navigating to a new row in a BindingSource).
• BindingPositionChanged: Updates BindingNavigator controls with the current record index and total count.