tomevault-io Visual Basic Database Patterns
ADO.NET and Entity Framework patterns for VB.NET with focus on connection management, parameterized queries, and async operations.
ADO.NET Patterns
Connection Management
' ✅ Good: Using statement ensures disposal
Public Async Function GetCustomersAsync() As Task(Of List(Of Customer))
Dim customers = New List(Of Customer)()
Using connection = New SqlConnection(connectionString)
Await connection.OpenAsync()
Using command = New SqlCommand("SELECT * FROM Customers WHERE IsActive = @isActive", connection)
command.Parameters.AddWithValue("@isActive", True)
Using reader = Await command.ExecuteReaderAsync()
While Await reader.ReadAsync()
customers.Add(New Customer With {
.Id = reader.GetInt32(0),
.Name = reader.GetString(1),
.Email = reader.GetString(2)
})
End While
End Using
End Using
End Using
Return customers
End Function
Parameterized Queries (Critical for SQL Injection Prevention)
' ✅ Good: Parameterized query
Public Async Function FindCustomerAsync(email As String) As Task(Of Customer)
Using connection = New SqlConnection(connectionString)
Await connection.OpenAsync()
Dim sql = "SELECT * FROM Customers WHERE Email = @email"
Using command = New SqlCommand(sql, connection)
command.Parameters.Add("@email", SqlDbType.NVarChar, 255).Value = email
Using reader = Await command.ExecuteReaderAsync()
If Await reader.ReadAsync() Then
Return MapCustomer(reader)
End If
End Using
End Using
End Using
Return Nothing
End Function
' ❌ BAD: String concatenation (SQL injection risk!)
Dim sql = $"SELECT * FROM Customers WHERE Email = '{email}'" ' NEVER DO THIS!
Transaction Management
Public Async Function TransferFundsAsync(fromAccountId As Integer, toAccountId As Integer, amount As Decimal) As Task
Using connection = New SqlConnection(connectionString)
Await connection.OpenAsync()
Using transaction = connection.BeginTransaction()
Try
' Debit from account
Using command = New SqlCommand("UPDATE Accounts SET Balance = Balance - @amount WHERE Id = @id", connection, transaction)
command.Parameters.AddWithValue("@amount", amount)
command.Parameters.AddWithValue("@id", fromAccountId)
Await command.ExecuteNonQueryAsync()
End Using
' Credit to account
Using command = New SqlCommand("UPDATE Accounts SET Balance = Balance + @amount WHERE Id = @id", connection, transaction)
command.Parameters.AddWithValue("@amount", amount)
command.Parameters.AddWithValue("@id", toAccountId)
Await command.ExecuteNonQueryAsync()
End Using
transaction.Commit()
Catch ex As Exception
transaction.Rollback()
Throw
End Try
End Using
End Using
End Function
Bulk Operations
Public Async Function BulkInsertCustomersAsync(customers As List(Of Customer)) As Task
Using connection = New SqlConnection(connectionString)
Await connection.OpenAsync()
' Create DataTable
Dim table = New DataTable()
table.Columns.Add("Name", GetType(String))
table.Columns.Add("Email", GetType(String))
table.Columns.Add("CreatedAt", GetType(DateTime))
For Each customer In customers
table.Rows.Add(customer.Name, customer.Email, DateTime.Now)
Next
' Bulk copy
Using bulkCopy = New SqlBulkCopy(connection)
bulkCopy.DestinationTableName = "Customers"
bulkCopy.BatchSize = 1000
Await bulkCopy.WriteToServerAsync(table)
End Using
End Using
End Function
Entity Framework Core Patterns
DbContext Setup
Public Class AppDbContext
Inherits DbContext
Public Property Customers As DbSet(Of Customer)
Public Property Orders As DbSet(Of Order)
Public Sub New(options As DbContextOptions(Of AppDbContext))
MyBase.New(options)
End Sub
Protected Overrides Sub OnModelCreating(builder As ModelBuilder)
' Configure entity
builder.Entity(Of Customer)(Sub(entity)
entity.HasKey(Function(c) c.Id)
entity.Property(Function(c) c.Name).IsRequired().HasMaxLength(200)
entity.Property(Function(c) c.Email).IsRequired().HasMaxLength(255)
entity.HasIndex(Function(c) c.Email).IsUnique()
End Sub)
' Configure relationship
builder.Entity(Of Order)(Sub(entity)
entity.HasOne(Function(o) o.Customer) _
.WithMany(Function(c) c.Orders) _
.HasForeignKey(Function(o) o.CustomerId)
End Sub)
End Sub
End Class
CRUD Operations
Public Class CustomerRepository
Private ReadOnly context As AppDbContext
Public Sub New(context As AppDbContext)
Me.context = context
End Sub
' Create
Public Async Function AddAsync(customer As Customer) As Task(Of Customer)
context.Customers.Add(customer)
Await context.SaveChangesAsync()
Return customer
End Function
' Read
Public Async Function GetByIdAsync(id As Integer) As Task(Of Customer)
Return Await context.Customers _
.Include(Function(c) c.Orders) _
.FirstOrDefaultAsync(Function(c) c.Id = id)
End Function
' Update
Public Async Function UpdateAsync(customer As Customer) As Task
context.Customers.Update(customer)
Await context.SaveChangesAsync()
End Function
' Delete
Public Async Function DeleteAsync(id As Integer) As Task
Dim customer = Await context.Customers.FindAsync(id)
If customer IsNot Nothing Then
context.Customers.Remove(customer)
Await context.SaveChangesAsync()
End If
End Function
' Query with filtering
Public Async Function GetActiveCustomersAsync() As Task(Of List(Of Customer))
Return Await context.Customers _
.Where(Function(c) c.IsActive) _
.OrderBy(Function(c) c.Name) _
.ToListAsync()
End Function
End Class
Async Queries
' Single result
Dim customer = Await context.Customers _
.FirstOrDefaultAsync(Function(c) c.Email = email)
' List results
Dim customers = Await context.Customers _
.Where(Function(c) c.IsActive) _
.ToListAsync()
' Count
Dim count = Await context.Customers.CountAsync()
' Any
Dim exists = Await context.Customers _
.AnyAsync(Function(c) c.Email = email)
' Aggregate
Dim totalOrders = Await context.Orders.SumAsync(Function(o) o.Amount)
Change Tracking
' Detach entity
context.Entry(customer).State = EntityState.Detached
' Track changes
Dim customer = Await context.Customers.FindAsync(id)
customer.Name = "Updated Name"
' See what changed
Dim entry = context.Entry(customer)
For Each prop In entry.Properties
If prop.IsModified Then
Console.WriteLine($"{prop.Metadata.Name}: {prop.OriginalValue} -> {prop.CurrentValue}")
End If
Next
Await context.SaveChangesAsync()
Database Migrations
Code-First Migrations
# Add migration
dotnet ef migrations add InitialCreate
# Update database
dotnet ef database update
# Rollback
dotnet ef database update PreviousMigration
# Generate SQL script
dotnet ef migrations script
Migration Class
Public Class CreateCustomersTable
Inherits Migration
Protected Overrides Sub Up(migrationBuilder As MigrationBuilder)
migrationBuilder.CreateTable(
name:="Customers",
columns:=Function(table) New With {
.Id = table.Column(Of Integer)(nullable:=False).Annotation("SqlServer:Identity", "1, 1"),
.Name = table.Column(Of String)(maxLength:=200, nullable:=False),
.Email = table.Column(Of String)(maxLength:=255, nullable:=False),
.CreatedAt = table.Column(Of DateTime)(nullable:=False)
},
constraints:=Sub(table)
table.PrimaryKey("PK_Customers", Function(x) x.Id)
table.UniqueConstraint("UK_Customers_Email", Function(x) x.Email)
End Sub
)
migrationBuilder.CreateIndex(
name:="IX_Customers_Email",
table:="Customers",
column:="Email",
unique:=True
)
End Sub
Protected Overrides Sub Down(migrationBuilder As MigrationBuilder)
migrationBuilder.DropTable(name:="Customers")
End Sub
End Class
Connection String Management
' appsettings.json
{
"ConnectionStrings": {
"DefaultConnection": "Server=(localdb)\\mssqllocaldb;Database=MyApp;Trusted_Connection=True;"
}
}
' Startup configuration
Public Class Startup
Public Sub ConfigureServices(services As IServiceCollection)
services.AddDbContext(Of AppDbContext)(Sub(options)
options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection"))
End Sub)
End Sub
End Class
Best Practices
✅ DO
' Use async methods
Dim customers = Await context.Customers.ToListAsync()
' Use parameterized queries
command.Parameters.AddWithValue("@email", email)
' Dispose connections
Using connection = New SqlConnection(connectionString)
End Using
' Use transactions for multiple operations
Using transaction = connection.BeginTransaction()
' Use IQueryable for deferred execution
Dim query As IQueryable(Of Customer) = context.Customers.Where(Function(c) c.IsActive)
❌ DON'T
' Don't concatenate SQL (SQL injection!)
Dim sql = $"SELECT * FROM Users WHERE Email = '{email}'"
' Don't forget to dispose
Dim connection = New SqlConnection(connectionString) ' No Using - leak!
' Don't block on async
Dim result = GetDataAsync().Result ' Deadlock risk
' Don't load entire table when filtering
Dim customers = context.Customers.ToList().Where(Function(c) c.IsActive) ' Loads all first!
' Better: context.Customers.Where(Function(c) c.IsActive).ToList()
Related Skills
- vb-core: Core VB.NET patterns
- vb-winforms: Windows Forms with database binding
- test-driven-development: Testing database operations
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