Tutorials ADO.NET Core Tutorial

Connection Strings — Complete Guide

Connection Strings — Complete Guide: free step-by-step lesson with examples, common mistakes, and interview tips — part of ADO.NET Core Tutorial on Toolliyo Academy.

8 min read Updated 8/22/2026

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ADO.NET Core Tutorial · Lesson 5 of 100

Connection Strings

Foundations → SQL & safety → Production → Projects

Foundations · 1 — Connections & CRUD · ~6 min · Module 1: ADO.NET Fundamentals

What is this?

A connection string names server, database, auth, and pool options that SqlConnection uses.

Why should you care?

Wrong strings are the #1 “works on my machine” failure for ShopNest deploys.

See it live — copy this example

Use a .NET console or API project with SQL Server LocalDB. Run dotnet run after pasting.

// appsettings.json
// "ConnectionStrings": { "ShopNestDb": "Server=(localdb)\mssqllocaldb;Database=ShopNestDb;Trusted_Connection=True;TrustServerCertificate=True;Encrypt=True" }
var cs = config.GetConnectionString("ShopNestDb");
Console.WriteLine(cs!.Contains("ShopNestDb"));

What happened?

Keep secrets out of source.
Prefer config + User Secrets/Key Vault.
Encrypt=True for modern clients.

Practice next

Put the string in appsettings.Development.json.
Read via IConfiguration.
Never commit passwords.
Add Max Pool Size=50.
Switch to Docker host name.

Remember

Config, not constants. Encrypt when possible. One name: ShopNestDb.

ShopNest config wiring

API reads ShopNestDb from configuration.

Outcome: Staging/prod only swap secrets.

Interview prep for this lesson

Practice these questions aloud after reading—each links to a full structured answer.

Mid PDF Detailed

Bind the data to the GridView. Example: protected void Page_Load(object sender, EventArgs e) { if (!IsPostBack) { SqlConnection connection = new SqlConnection(connectionString); SqlDataAdapter adapter = new SqlDataAdapter("SELECT CustomerID, CustomerName FROM Customers", connection); DataTable dataTable = new DataTable();

Short answer: dapter.Fill(dataTable); GridView1.DataSource = dataTable; GridView1.DataBind(); } } Here, GridView1 is bound to the data returned from the SQL query (SELECT CustomerID, CustomerName FROM Customers), and the…

Mid PDF Detailed

It uses SQL commands to retrieve and update data. Example: SqlDataAdapter adapter = new SqlDataAdapter("SELECT * FROM Customers", connection); DataSet dataset = new DataSet();

Short answer: dapter.Fill(dataset, "Customers"); // Populates the DataSet with data from the "Customers" table dapter.Fill(dataset, "Customers"); // Populates the DataSet with data from the…

Mid PDF Detailed

Use the DataAdapter's Update() method to push the changes back to the database. Example: SqlDataAdapter adapter = new SqlDataAdapter("SELECT * FROM Customers", connection); SqlCommandBuilder commandBuilder = new SqlCommandBuilder(adapter); // Automatically generates insert, update, delete commands DataSet dataset = new DataSet();

Short answer: dapter.Fill(dataset, "Customers"); // Modify data in the DataSet dataset.Tables["Customers"].Rows[0]["CustomerName"] = "New Name"; // Update the database with the mod…

Mid PDF Detailed

Closing the connection with the Close() method to release resources.?

Short answer: Example: using (SqlConnection connection = new SqlConnection(connectionString)) { connection.Open(); // Execute commands here connection.Close(); } Example code Example: using (SqlConnection connection = ne…

Mid PDF Detailed

Call the Update method on the DataAdapter to sync changes. Example: // Assuming you already have a populated DataTable DataTable table = new DataTable(); SqlDataAdapter adapter = new SqlDataAdapter("SELECT * FROM Customers", connection); // Set commands for Insert, Update, and Delete

Short answer: dapter.UpdateCommand = new SqlCommand("UPDATE Customers SET CustomerName = @CustomerName WHERE CustomerID = @CustomerID", connection); dapter.UpdateCommand.Parameters.Add("@CustomerName"…

All course Q&A Practice exams

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