Collection of datastores for use with the Google APIs .net Client

DatabaseDatastore.cs

using Google.Apis.Json;
using Google.Apis.Util.Store;
using System;
using System.Data.Common;
using System.Threading.Tasks;

namespace GoogleAuthDataStores
{
    /// <summary>
    /// Database data store that implements <see cref="IDataStore"/>. This store creates a different row for each
    /// combination of type and key. This file data store stores a JSON format of the specified object.
    /// </summary>
    internal abstract class DatabaseDatastore : IDataStore
    {
        /// <summary>Represents a connection to a database. </summary>
        public virtual DbConnection Connection { get; set; }

        /// <summary>Represents an SQL statement or stored procedure to execute against a data source.
        ///          Provides a base class for database-specific classes that represent commands.</summary>
        public virtual DbCommand Command { get; set; }

        /// <summary>The string used to open the connection.</summary>
        public virtual string ConnectionString { get; set; }

        public string CredentialsTableName { get; private set; }

        /// <summary>
        /// Creates a new table in the data base if the Users table does not exist within the database used in the connectionstring.
        /// </summary>
        /// <param name="connectionString">The string used to open the connection.</param>
        public DatabaseDatastore(string connectionString, string tableName = null)
        {
            CredentialsTableName = tableName;

            if (string.IsNullOrEmpty(CredentialsTableName))
                CredentialsTableName = "GoogleUserCredentials";

            ConnectionString = connectionString;
            if (!DoesUserTableExist())
            {
                Command.CommandType = System.Data.CommandType.Text;
                Command.CommandText = string.Format("CREATE TABLE [{0}]([UserId][nvarchar](100) NOT NULL,[Credentials] [nvarchar](2000) NOT NULL)", CredentialsTableName);
                Command.Connection.Open();
                Command.ExecuteNonQueryAsync();
                Command.Connection.Close();
            }
        }

        /// <summary>
        /// Stores the given value for the given key. It creates a new row in the database with the user id of
        /// (primary key <see cref="GenerateStoredKey"/>) in <see cref="CredentialsTableName"/>.
        /// </summary>
        /// <typeparam name="T">The type to store in the data store.</typeparam>
        /// <param name="key">The key.</param>
        /// <param name="value">The value to store in the data store.</param>
        Task IDataStore.StoreAsync<T>(string key, T value)
        {
            if (string.IsNullOrEmpty(key))
            {
                throw new ArgumentException("Key MUST have a value");
            }

            var serialized = NewtonsoftJsonSerializer.Instance.Serialize(value);
            save(GenerateStoredKey(key, typeof(T)), serialized);
            return Task.Delay(0);
        }

        /// <summary>
        /// Deletes the given key. It deletes the <see cref="GenerateStoredKey"/> row in
        /// <see cref="CredentialsTableName"/>.
        /// </summary>
        /// <param name="key">The key to delete from the data store.</param>
        Task IDataStore.DeleteAsync<T>(string key)
        {
            if (string.IsNullOrEmpty(key))
            {
                throw new ArgumentException("Key MUST have a value");
            }

            try
            {
                Command.CommandType = System.Data.CommandType.Text;
                Command.CommandText = string.Format("delete from {0} where userid = '{1}'", CredentialsTableName, GenerateStoredKey(key, typeof(T)));
                Command.Connection.Open();
                Command.ExecuteNonQueryAsync();
                Command.Connection.Close();
            }
            catch (System.Data.SqlClient.SqlException ex)
            {
                if (Command.Connection.State == System.Data.ConnectionState.Open)
                    Command.Connection.Close();

                throw new Exception("Failed to delete credentials", ex);
            }

            return Task.Delay(0);
        }

        /// <summary>
        /// Returns the stored value for the given key or <c>null</c> if the matching row (<see cref="GenerateStoredKey"/>
        /// in <see cref="CredentialsTableName"/> doesn't exist.
        /// </summary>
        /// <typeparam name="T">The type to retrieve.</typeparam>
        /// <param name="key">The key to retrieve from the data store.</param>
        /// <returns>The stored object.</returns>
        Task<T> IDataStore.GetAsync<T>(string key)
        {
            if (string.IsNullOrEmpty(key))
            {
                throw new ArgumentException("Key MUST have a value");
            }

            TaskCompletionSource<T> tcs = new TaskCompletionSource<T>();
            var credentials = GetUserByKey(GenerateStoredKey(key, typeof(T)));
            if (credentials != null)
            {
                try
                {
                    tcs.SetResult(NewtonsoftJsonSerializer.Instance.Deserialize<T>(credentials));
                }
                catch (Exception ex)
                {
                    tcs.SetException(ex);
                }
            }
            else
            {
                tcs.SetResult(default(T));
            }
            return tcs.Task;
        }

        /// <summary>
        /// Clears all values in the data store. This method deletes all files in <see cref="CredentialsTableName"/>.
        /// </summary>
        Task IDataStore.ClearAsync()
        {
            try
            {
                Command.CommandType = System.Data.CommandType.Text;
                Command.CommandText = "truncate table " + CredentialsTableName;
                Command.Connection.Open();
                DbDataReader reader = Command.ExecuteReader();
                reader.Close();
                Command.Connection.Close();
            }
            catch (System.Data.SqlClient.SqlException ex)
            {
                throw new Exception("Failed to clear credentials", ex);
            }

            return Task.Delay(0);
        }

        /// <summary>
        /// Checks if the table exits <see cref="CredentialsTableName"/>.
        /// </summary>
        private bool DoesUserTableExist()
        {
            try
            {
                Command.CommandType = System.Data.CommandType.Text;
                Command.CommandText = "select * from " + CredentialsTableName;
                Command.Connection.Open();
                DbDataReader reader = Command.ExecuteReader();
                reader.Close();
                Command.Connection.Close();
                return true;
            }
            catch (System.Data.SqlClient.SqlException)
            {
                Command.Connection.Close();
                return false;
            }
        }

        /// <summary>
        /// Checks if the user exists <see cref="GenerateStoredKey"/>.
        /// </summary>
        private string GetUserByKey(string key)
        {
            try
            {
                string credentials = string.Empty;
                Command.CommandType = System.Data.CommandType.Text;
                Command.CommandText = string.Format("select Credentials from {0} where userid = '{1}'", CredentialsTableName, key);
                Command.Connection.Open();
                DbDataReader reader = Command.ExecuteReader();
                if (reader.HasRows)
                {
                    reader.Read();
                    credentials = reader[0].ToString();
                }

                reader.Close();
                Command.Connection.Close();

                if (string.IsNullOrEmpty(credentials))
                    return null;

                return credentials;
            }
            catch (System.Data.SqlClient.SqlException)
            {
                if (Command.Connection.State == System.Data.ConnectionState.Open)
                    Command.Connection.Close();
                return null;
            }
        }

        /// <summary>
        /// Save the credentials.  If the user <see cref="GenerateStoredKey"/> does not exists we insert it other wise we will do an update.
        /// </summary>
        /// <param name="key"></param>
        /// <param name="serialized"></param>
        private void save(string key, string serialized)
        {
            try
            {
                if (GetUserByKey(key) == null)
                {
                    Command.CommandText = string.Format("insert into {0} (userid, Credentials) values ('{1}','{2}') ", CredentialsTableName, key, serialized);
                }
                else
                {
                    Command.CommandText = string.Format("update {0}  set Credentials = '{1}' where key = '{2}'", CredentialsTableName, serialized, key);
                }

                Command.CommandType = System.Data.CommandType.Text;
                Command.Connection.Open();
                Command.ExecuteReader();
                Command.Connection.Close();
            }
            catch (System.Data.SqlClient.SqlException ex)
            {
                if (Command.Connection.State == System.Data.ConnectionState.Open)
                    Command.Connection.Close();
                throw ex;
            }
        }

        /// <summary>Creates a unique stored key based on the key and the class type.</summary>
        /// <param name="key">The object key.</param>
        /// <param name="t">The type to store or retrieve.</param>
        public static string GenerateStoredKey(string key, Type t)
        {
            return string.Format("{0}-{1}", t.FullName, key);
        }
    }
}

EntityFrameworkDataStore.cs

using Google.Apis.Json;
using Google.Apis.Util.Store;
using System;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using System.Data.Entity;
using System.Linq;
using System.Reflection;
using System.Threading.Tasks;

namespace GoogleAuthDataStores
{
    public class GoogleUserCredential
    {
        [Key]
        public int ID { get; set; }

        [Required, Index(IsUnique = true), StringLength(500)]
        public string Key { get; set; }

        [Required]
        public string Credentials { get; set; }
    }

    internal class EntityFrameworkDataStore : DbContext, IDataStore
    {
        public DbSet<GoogleUserCredential> GoogleUserCredentials { get; set; }

        /// <summary>The string used to open the connection.</summary>
        public virtual string ConnectionString { get; set; }

        /// <summary>
        /// Creates a new table in the data base if the Users table does not exist within the database used in the connectionstring.
        /// </summary>
        /// <param name="connectionString">The string used to open the connection.</param>
        public EntityFrameworkDataStore(string connectionString) : base(connectionString)
        {
            ConnectionString = connectionString;
        }

        /// <summary>
        /// Stores the given value for the given key. It creates a new row in the database with the user id of
        /// (primary key <see cref="GenerateStoredKey"/>) in <see cref="GoogleUserCredentials"/>.
        /// </summary>
        /// <typeparam name="T">The type to store in the data store.</typeparam>
        /// <param name="key">The key.</param>
        /// <param name="value">The value to store in the data store.</param>
        Task IDataStore.StoreAsync<T>(string key, T value)
        {
            if (string.IsNullOrEmpty(key))
            {
                throw new ArgumentException("Key MUST have a value");
            }

            var serialized = NewtonsoftJsonSerializer.Instance.Serialize(value);
            save(GenerateStoredKey(key), serialized);
            return Task.Delay(0);
        }

        /// <summary>
        /// Deletes the given key. It deletes the <see cref="GenerateStoredKey"/> row in
        /// <see cref="GoogleUserCredentials"/>.
        /// </summary>
        /// <param name="key">The key to delete from the data store.</param>
        Task IDataStore.DeleteAsync<T>(string key)
        {
            if (string.IsNullOrEmpty(key))
            {
                throw new ArgumentException("Key MUST have a value");
            }

            try
            {
                var hold = GoogleUserCredentials.Where(a => a.Key == key).FirstOrDefault();
                GoogleUserCredentials.Remove(hold);
                SaveChangesAsync();
            }
            catch (System.Data.SqlClient.SqlException ex)
            {
                throw new Exception("Failed to delete credentials", ex);
            }

            return Task.Delay(0);
        }

        /// <summary>
        /// Returns the stored value for the given key or <c>null</c> if the matching row (<see cref="GenerateStoredKey"/>
        /// in <see cref="GoogleUserCredentials"/> doesn't exist.
        /// </summary>
        /// <typeparam name="T">The type to retrieve.</typeparam>
        /// <param name="key">The key to retrieve from the data store.</param>
        /// <returns>The stored object.</returns>
        Task<T> IDataStore.GetAsync<T>(string key)
        {
            if (string.IsNullOrEmpty(key))
            {
                throw new ArgumentException("Key MUST have a value");
            }

            TaskCompletionSource<T> tcs = new TaskCompletionSource<T>();
            var user = GetUserByKey(GenerateStoredKey(key));
            if (user != null)
            {
                try
                {
                    tcs.SetResult(NewtonsoftJsonSerializer.Instance.Deserialize<T>(user.Credentials));
                }
                catch (Exception ex)
                {
                    tcs.SetException(ex);
                }
            }
            else
            {
                tcs.SetResult(default(T));
            }
            return tcs.Task;
        }

        /// <summary>
        /// Clears all values in the data store. This method deletes all files in <see cref="GoogleUserCredentials"/>.
        /// </summary>
        Task IDataStore.ClearAsync()
        {
            try
            {
                foreach (var item in GoogleUserCredentials)
                {
                    GoogleUserCredentials.Remove(item);
                }
            }
            catch (System.Data.SqlClient.SqlException ex)
            {
                throw new Exception("Failed to clear credentials", ex);
            }

            return Task.Delay(0);
        }

        /// <summary>
        /// Checks if the user exists <see cref="GenerateStoredKey"/>.
        /// </summary>
        private GoogleUserCredential GetUserByKey(string key)
        {
            try
            {
                var user = GoogleUserCredentials.Where(a => a.Key == key).FirstOrDefault();

                if (user != null)
                    return user;

                return null;
            }
            catch (System.Data.SqlClient.SqlException)
            {
                return null;
            }
        }

        /// <summary>
        /// Save the credentials.  If the user <see cref="GenerateStoredKey"/> does not exists we insert it other wise we will do an update.
        /// </summary>
        /// <param name="key"></param>
        /// <param name="serialized"></param>
        private void save(string key, string serialized)
        {
            try
            {
                var user = GoogleUserCredentials.Where(a => a.Key == key).FirstOrDefault();
                if (user == null)
                {
                    var hold = new GoogleUserCredential { Key = key, Credentials = serialized };
                    GoogleUserCredentials.Add(hold);
                }
                else
                {
                    var aUser = this.GoogleUserCredentials.Where(a => a.Key == key).FirstOrDefault();
                    aUser.Credentials = serialized;
                }
                SaveChanges();
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }

        /// <summary>Creates a unique stored key based on the key and the current project name.</summary>
        /// <param name="key">The object key.</param>
        public static string GenerateStoredKey(string key)
        {
            return string.Format("{0}-{1}", Assembly.GetCallingAssembly().GetName().Name, key);
        }
    }
}

OleDBDataStore.cs

using System.Data.Common;
using System.Data.OleDb;
namespace GoogleAuthDataStores
{
    
        internal class OleDBDataStore : DatabaseDatastore
        {
            private DbConnection connection = null;
            private DbCommand command = null;


            public OleDBDataStore(string connectionString) : base(connectionString)
            {
                connection = Connection;
            }

            public override DbConnection Connection
            {
                get
                {
                    if (connection == null)
                    {

                        connection = new OleDbConnection(ConnectionString);
                    }

                    return connection;
                }
                set { connection = value; }
            }

            public override DbCommand Command
            {
                get
                {
                    if (connection == null)
                    {
                        command = new OleDbCommand();
                        command.Connection = Connection;
                    }

                    return command;
                }
                set { command = value; }
            }
        }
    }

SqlServerDatabase.cs

using System.Data.Common;
using System.Data.SqlClient;

namespace GoogleAuthDataStores
{
    internal class SqlServerDatabase : DatabaseDatastore
    {
        private DbConnection connection = null;
        private DbCommand command = null;
       

        public SqlServerDatabase(string connectionString) : base(connectionString){
            connection = Connection;
        }       

        public override DbConnection Connection
        {
            get
            {
                if (connection == null)
                {
                    
                    connection = new SqlConnection(ConnectionString);
                }

                return connection;
            }
            set { connection = value; }
        }

        public override DbCommand Command
        {
            get
            {
                if (connection == null)
                {
                    command = new SqlCommand();
                    command.Connection = Connection;
                }

                return command;
            }
            set { command = value; }
        }
    }
}

Using the DatabaseDatastore, is this autogenerated (i.e. is it worth creating a pull request?)

cannot use the Connection / Command objects in the constructor within the if (!DoesUserTableExist()) block as they haven't been initialised by that point (calling : base(connectionString) from the concrete class will call this section.

also
Command.CommandText = string.Format("update {0} set Credentials = '{1}' where key = '{2}'", CredentialsTableName, serialized, key);
should read
Command.CommandText = string.Format("update {0} set Credentials = '{1}' where UserId = '{2}'", CredentialsTableName, serialized, key);

No its wasn't auto generated. Feel free to fix it :)