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WritableServerSelector.cs
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WritableServerSelector.cs
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/* Copyright 2013-present MongoDB Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
using System.Collections.Generic;
using System.Linq;
using MongoDB.Driver.Core.Bindings;
using MongoDB.Driver.Core.Servers;
namespace MongoDB.Driver.Core.Clusters.ServerSelectors
{
/// <summary>
/// Represents a server selector that selects writable servers.
/// </summary>
public class WritableServerSelector : IServerSelector
{
#region static
// static fields
private readonly static WritableServerSelector __instance = new WritableServerSelector();
// static properties
/// <summary>
/// Gets a WritableServerSelector.
/// </summary>
/// <value>
/// A server selector.
/// </value>
public static WritableServerSelector Instance
{
get { return __instance; }
}
#endregion
// constructors
private readonly IMayUseSecondaryCriteria _mayUseSecondary;
/// <summary>
/// Initializes an instance of the WritableServerSelector class.
/// </summary>
public WritableServerSelector()
{
}
/// <summary>
/// Initializes an instance of the WritableServerSelector class.
/// </summary>
/// <param name="mayUseSecondary">The may use secondary criteria.</param>
public WritableServerSelector(IMayUseSecondaryCriteria mayUseSecondary)
{
_mayUseSecondary = mayUseSecondary; // can be null
}
// properties
/// <summary>
/// Returns the may use secondary criteria.
/// </summary>
public IMayUseSecondaryCriteria MayUseSecondary => _mayUseSecondary;
// methods
/// <inheritdoc/>
public IEnumerable<ServerDescription> SelectServers(ClusterDescription cluster, IEnumerable<ServerDescription> servers)
{
if (cluster.IsDirectConnection)
{
return servers;
}
var serversList = servers.ToList(); // avoid multiple enumeration
if (CanUseSecondaries(cluster, serversList))
{
var readPreferenceSelector = new ReadPreferenceServerSelector(_mayUseSecondary.ReadPreference);
return readPreferenceSelector.SelectServers(cluster, serversList);
}
if (_mayUseSecondary != null)
{
_mayUseSecondary.EffectiveReadPreference = ReadPreference.Primary; // fallback to primary
}
return serversList.Where(x => x.Type.IsWritable());
}
/// <inheritdoc/>
public override string ToString()
{
return "WritableServerSelector";
}
private bool CanUseSecondaries(ClusterDescription cluster, List<ServerDescription> servers)
{
if (_mayUseSecondary?.ReadPreference == null || servers.Count == 0)
{
return false;
}
switch (cluster.Type)
{
case ClusterType.ReplicaSet:
case ClusterType.Sharded:
return servers.All(s => _mayUseSecondary.CanUseSecondary(s));
case ClusterType.LoadBalanced:
return true;
default:
return false;
}
}
}
}