Table of Contents

PostgreSQL

This connector simplifies using PostgreSQL. Currently, the connector supports the Npgsql provider.

This connector provides an IHealthContributor, which you can use in conjunction with the Steeltoe Management Health check endpoint.

Usage

You should know how the .NET Configuration service works before starting to use the connector. You need a basic understanding of ConfigurationBuilder and how to add providers to the builder to configure the connector.

You should also know how the ASP.NET Core Startup class is used to configure the application services for the app. Pay particular attention to the ConfigureServices() method.

To use this connector:

  1. Create a PostgreSQL Service instance and bind it to your application.
  2. Optionally, Configure any PostgreSQL client settings (such as appsettings.json).
  3. Optionally, add the Steeltoe Cloud Foundry config provider to your ConfigurationBuilder.
  4. Add NpgsqlConnection or DbContext to your IServiceCollection.

Add NuGet Reference

To use the PostgreSQL connector, add your choice of PostgreSQL package between Npgsql and Npgsql.EntityFrameworkCore.PostgreSQL as you would if you were not using Steeltoe. Then add a reference to the appropriate Steeltoe Connector NuGet package.

Steeltoe does not currently include direct support for PostgreSQL with Entity Framework 6.

Configure Settings

The PostgreSQL connector supports several settings for creating the NpgsqlConnection to a database. This can be useful when you develop and test an application locally and need to configure the connector for non-default settings.

The following example shows a PostgreSQL connector configuration (in JSON) to set up a connection to a database at myserver:5432:

{
  ...
  "Postgres": {
    "Client": {
      "Host": "myserver",
      "Port": 5432
    }
  }
  ...
}

The following table describes all of the possible settings for the connector:

Key Description Default
Host Hostname or IP Address of server. localhost
Port Port number of server. 5432
Username Username for authentication. not set
Password Password for authentication. not set
Database Schema to which to connect. not set
ConnectionString Full connection string. Built from settings

IMPORTANT: All of these settings should be prefixed with Postgres:Client:.

The samples and most templates are already set up to read from appsettings.json.

If a ConnectionString is provided and VCAP_SERVICES are not detected (a typical scenario for local application development), the ConnectionString is used exactly as provided.

Cloud Foundry

To use PostgreSQL on Cloud Foundry, after a PostgreSQL service is installed, you can create and bind an instance of it to your application by using the Cloud Foundry CLI:

# Create PostgreSQL service
cf create-service EDB-Shared-PostgreSQL "Basic PostgreSQL Plan" myPostgres

# Bind service to `myApp`
cf bind-service myApp myPostgres

# Restage the app to pick up change
cf restage myApp

The preceding commands work for the PostgreSQL service provided by EDB on Cloud Foundry. For another service, adjust the create-service command to fit your environment.

This connector also works with the Azure Service Broker.

Once the service is bound to your application, the connector's settings are available in VCAP_SERVICES.

Add NpgsqlConnection

To use a NpgsqlConnection in your application, add it to the service container in the ConfigureServices() method of the Startup class:

using Steeltoe.Connector.PostgreSql;

public class Startup {
    ...
    public IConfiguration Configuration { get; private set; }
    public Startup(...)
    {
      ...
    }
    public void ConfigureServices(IServiceCollection services)
    {
        // Add NpgsqlConnection
        services.AddPostgresConnection(Configuration);

        // Add framework services.
        services.AddMvc();
        ...
    }
    ...
}

The AddPostgresConnection(Configuration) method call configures the NpgsqlConnection by using the configuration built by the application and adds the connection to the service container.

By default, this extension method will automatically configure an IHealthContributor to report the health of this database connection. This behavior can be turned off by passing false for the parameter addSteeltoeHealthChecks

Use NpgsqlConnection

Once the connection is configured and added to the service container, you can inject it and use it in a controller or a view:

using Npgsql;
...
public class HomeController : Controller
{
    public IActionResult PostgresData([FromServices] NpgsqlConnection dbConnection)
    {
        dbConnection.Open();

        NpgsqlCommand cmd = new NpgsqlCommand("SELECT * FROM TestData;", dbConnection);
        var rdr = cmd.ExecuteReader();

        while (rdr.Read())
        {
            ViewData["Key" + rdr[0]] = rdr[1];
        }

        rdr.Close();
        dbConnection.Close();

        return View();
    }
}

Add DbContext

To use Entity Framework, inject and use a DbContext in your application instead of a NpgsqlConnection through the AddDbContext<>() method:

using Steeltoe.Connector.PostgreSql.EFCore;

public class Startup {
    public IConfiguration Configuration { get; private set; }
    public Startup(...)
    {
      ...
    }
    public void ConfigureServices(IServiceCollection services)
    {
        // Add EFCore TestContext configured with a PostgreSQL configuration
        services.AddDbContext<TestContext>(options => options.UseNpgsql(Configuration));

        // see note below explaining AddPostgresHealthContributor
        services.AddPostgresHealthContributor(Configuration);
        ...
    }
}

The AddDbContext<TestContext>(options => options.UseNpgsql(Configuration)); method call configures the TestContext by using the configuration built by the application and adds the context to the service container.

This extension method will NOT automatically configure an IHealthContributor to report the health of this database connection. The package Steeltoe.Connector.ConnectorCore provides an IServiceCollection extension method that will. Directly add the health contributor with the code services.AddPostgresHealthContributor(Configuration)

The following example shows how you would define the DbContext:

using Microsoft.EntityFrameworkCore;
...

public class TestContext : DbContext
{
    public TestContext(DbContextOptions options) : base(options)
    {
    }
    public DbSet<TestData> TestData { get; set; }
}

If you need to set additional properties for the DbContext like MigrationsAssembly or connection retry settings, create an Action<NpgsqlDbContextOptionsBuilder>:

Action<NpgsqlDbContextOptionsBuilder> npgsqlOptionsAction = (o) =>
{
  o.MigrationsAssembly(typeof(Startup).GetTypeInfo().Assembly.GetName().Name);
  // Configuring Connection Resiliency: https://docs.microsoft.com/ef/core/miscellaneous/connection-resiliency
  o.EnableRetryOnFailure(maxRetryCount: 15, maxRetryDelay: TimeSpan.FromSeconds(30), errorNumbersToAdd: null);
};

Pass your new options action into the AddDbContext method:

services.AddDbContext<TestContext>(options => options.UseNpgsql(Configuration, npgsqlOptionsAction));

Use DbContext

Once you have configured and added the context to the service container, you can inject it and use it in a controller or a view:

using Project.Models;
...
public class HomeController : Controller
{
    public IActionResult PostgresData([FromServices] TestContext context)
    {
        return View(context.TestData.ToList());
    }
}
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