DatabaseDependency Class

Definition

Namespace

Cuemon.Data

Assemblies

Cuemon.Data.dll

Source

src/Cuemon.Data/DatabaseDependency.cs

Provides a way to monitor any changes occurred to one or more relational data sources while notifying subscribing objects.

public class DatabaseDependency : Dependency, IDependency

Inheritance

object

Dependency

DatabaseDependency

Implements

IDependency

Inherited Members

Dependency.DependencyChanged

Dependency.BreakTieOnChanged

Dependency.UtcLastModified

Dependency.HasChanged

Dependency.SetUtcLastModified(DateTime)

Dependency.OnDependencyChangedRaised(DependencyEventArgs)

Dependency.Start()

Dependency.StartAsync()

Dependency.OnWatcherChanged(object, WatcherEventArgs)

Examples

The following example demonstrates how to use to monitor a relational data source for changes and notify dependent objects. It sets up a Lazy<DatabaseWatcher> with a stub connection and a command that executes SELECT COUNT(*) FROM Products, then creates a DatabaseDependency with a change event handler that writes to the console. The dependency is started asynchronously, showing how to watch a relational data source for data-change notifications.

using System;
using System.Data;
using System.Threading.Tasks;
using Cuemon.Data;
using Cuemon.Runtime;

namespace MyApp.Examples;

public class DatabaseDependencyExample
{
    public async Task DemonstrateAsync()
    {
        var lazyWatcher = new Lazy<DatabaseWatcher>(() =>
        {
            var connection = new StubConnection();
            return new DatabaseWatcher(
                connection,
                conn =>
                {
                    var command = conn.CreateCommand();
                    command.CommandText = "SELECT COUNT(*) FROM Products";
                    return command.ExecuteReader();
                });
        });

        var dependency = new DatabaseDependency(lazyWatcher, breakTieOnChanged: true);

        dependency.DependencyChanged += (sender, args) =>
        {
            Console.WriteLine("Database data has changed!");
        };

        await dependency.StartAsync();
    }

    private sealed class StubConnection : IDbConnection
    {
        public string ConnectionString { get; set; }
        public int ConnectionTimeout => 30;
        public string Database => "MyDb";
        public ConnectionState State => ConnectionState.Closed;
        public IDbTransaction BeginTransaction() => null;
        public IDbTransaction BeginTransaction(IsolationLevel il) => null;
        public void ChangeDatabase(string databaseName) { }
        public void Close() { }
        public IDbCommand CreateCommand() => new StubCommand();
        public void Open() { }
        public void Dispose() { }
    }

    private sealed class StubCommand : IDbCommand
    {
        public string CommandText { get; set; }
        public int CommandTimeout { get; set; }
        public CommandType CommandType { get; set; }
        public IDbConnection Connection { get; set; }
        public IDataParameterCollection Parameters => null;
        public IDbTransaction Transaction { get; set; }
        public UpdateRowSource UpdatedRowSource { get; set; }
        public bool DesignTimeVisible { get; set; }
        public void Cancel() { }
        public IDbDataParameter CreateParameter() => null;
        public int ExecuteNonQuery() => 0;
        public IDataReader ExecuteReader() => null;
        public IDataReader ExecuteReader(CommandBehavior behavior) => null;
        public object ExecuteScalar() => 0;
        public void Prepare() { }
        public void Dispose() { }
    }
}

Constructors

Name	Description
DatabaseDependency(IEnumerable<Lazy<DatabaseWatcher>>, bool)	Initializes a new instance of the DatabaseDependency class.
DatabaseDependency(Lazy<DatabaseWatcher>, bool)	Initializes a new instance of the DatabaseDependency class.

See Also

Dependency