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I'm failing to connect to PostgreSQL using Npgsql in my local environment I have checked each and every thing looks fine and I'm able to connect using my pgAmin and also I have managed to update tables after creating migrations I don't know where I'm doing it wrong where I try to open the connection so as I can insert data into the table I have created below is my implementation.

What I have tried:

  "ConnectionStrings": {
    "DefaultConnection": "Host=localhost;Port=5432;Database=customerdb;Username=postgres;Password=admin123;"
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
  "AllowedHosts": "*"

Controller method to insert data

private readonly string _connectionString;

  public DataLoader(string connectionString)
  _connectionString = connectionString;

    public async Task LoadToDatabase(IEnumerable<Customer> data)
             await using var connection = new NpgsqlConnection(_connectionString);
             await connection.OpenAsync();
             foreach (var customerDetails in data)
             await connection.ExecuteAsync("INSERT INTO Customer (CustomerCode, CustomerNames,OrderId, Location) VALUES (@CustomerCode, @CustomerNames, @OrderId, @Location)", customerDetails);
             await connection.CloseAsync();
         catch (NpgsqlException ex)
             // Log error (log to a file, console, etc.)
             Console.WriteLine($"Error opening PostgreSQL connection: {ex.Message}");
         catch (Exception ex)
             // Log error (log to a file, console, etc.)
             Console.WriteLine($"An error occurred: {ex.Message}");

Program .CS class
// Add services to the container. builder.Services.AddControllers();

// Adding configuration builder.Configuration.AddJsonFile("appsettings.json", optional: false, reloadOnChange: true);

// Getting the configuration
var configuration = builder.Configuration;

// Retrieving connection string from configuration
var postgreconnection = configuration.GetSection("ConnectionStrings:DefaultConnection").Value;

// Configuring PostgreSQL Database connection
builder.Services.AddDbContext<ApplicationDbContext>(options =>options.UseNpgsql(postgreconnection));

// Learn more about configuring Swagger/OpenAPI at

builder.Services.AddSingleton(new DataExtractor());
builder.Services.AddSingleton(new DataTransformer());
builder.Services.AddSingleton(new DataLoader(postgreconnection));

1 solution

If memory serves, it's User ID, not username. You need to correct your connection string.

Edit: Looking at the insert statement, I see that you haven't supplied SqlParameters. Try mapping the properties from your customer class as sql parameters, and pass that to your command instead.
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Office Systems 10-Jun-24 7:49am    
Thanks @Pete O'Hanlon for your response however I have tried using User ID but still it fails to establish connection with postgresql database, and the other thing that I'm getting confused is why it has managed to create database in postgresql using the same connection string after adding migration but trying to open connection with Npgsql it fails
Pete O'Hanlon 10-Jun-24 8:30am    
I've just gone back to another project I was working on. Username is correct if you're using EntityFramework; but it appears that you're trying to use EntityFramework and direct access here. If you are, why are you mixing these together? Here's an example of a context class that I use with an EF project:

using Microsoft.EntityFrameworkCore;
using Qip.Models;

namespace Qip.Server.EntityFramework;

public class QipContext(IConfiguration configuration) : DbContext
private readonly string connectionString =
configuration.GetConnectionString("Qip") ?? throw new ArgumentException("Connection String");

/// The release labels.

public DbSet<releaselabel>? Labels { get; set; }

public DbSet<project>? Projects { get; set; }

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)

protected override void OnModelCreating(ModelBuilder modelBuilder)
modelBuilder.Entity<releaselabel>().HasIndex(p => p.Label);

private void OnModelCreating<t>(ModelBuilder modelBuilder) where T : ModelBase
modelBuilder.Entity<t>().Property(p => p.Id).ValueGeneratedOnAdd();

Using it (in a minimal API controller) is as simple as this:

labelsVersion1Api.MapPost("/label/{label}", async (QipContext context, string label) =>
ReleaseLabel releaseLabel = new ReleaseLabel { Label = label };
await context.SaveChangesAsync();
return TypedResults.Created("/labels", releaseLabel);
Pete O'Hanlon 10-Jun-24 9:26am    
I noticed something about your controller - I have updated the answer to query why you aren't using SqlParameters in your call.
Maciej Los 10-Jun-24 10:22am    
Pete O'Hanlon 10-Jun-24 10:42am    

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