c# - 有没有办法创建或更新 MongoDB 索引？

Question

根据 createIndexes command 上的文档:

If you create an index with one set of options and then issue createIndexes with the same index fields but different options, MongoDB will not change the options nor rebuild the index.

解决方案是删除索引并从头开始创建它，但成本很高。

有没有办法在没有索引的情况下创建索引，如果有具有相同选项的索引则什么也不做，如果选项发生变化则替换索引？

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这个问题最初是由 Phil Barresi 提出的here但已被删除。

Answer 1

查看 driver我已经实现了一个 CreateOrUpdateIndex 扩展方法，它比较原始索引文档，如果索引选项已更改，则索引将被替换(只要索引名称保持不变):

public static WriteConcernResult CreateOrUpdateIndex(
    this MongoCollection mongoCollection,
    IMongoIndexKeys keys,
    IMongoIndexOptions options = null)
{
    if (mongoCollection.IndexExists(keys))
    {
        var indexDocument = mongoCollection.GenerateIndexDocument(keys, options);
        if (!mongoCollection.GetIndexes().RawDocuments.Any(indexDocument.Equals))
        {
            mongoCollection.DropIndex(keys);
        }
    }

    return mongoCollection.CreateIndex(keys, options);
}

生成原始索引文档:

public static BsonDocument GenerateIndexDocument(this MongoCollection mongoCollection, IMongoIndexKeys keys, IMongoIndexOptions options)
{
    var optionsDocument = options.ToBsonDocument();
    var keysDocument = keys.ToBsonDocument();
    var indexDocument = new BsonDocument
    {
        { "ns", mongoCollection.FullName },
        { "name", GenerateIndexName(keysDocument, optionsDocument) },
        { "key", keysDocument }
    };
    if (optionsDocument != null)
    {
        indexDocument.Merge(optionsDocument);
    }

    return indexDocument;
}

public static string GenerateIndexName(IEnumerable<BsonElement> keys, BsonDocument options)
{
    const string name = "name";
    if (options != null && options.Contains(name)) return options[name].AsString;

    return string.Join("_", keys.Select(element =>
    {
        var value = "x";
        switch (element.Value.BsonType)
        {
            case BsonType.Int32: value = ((BsonInt32)element.Value).Value.ToString(); break;
            case BsonType.Int64: value = ((BsonInt64)element.Value).Value.ToString(); break;
            case BsonType.Double: value = ((BsonDouble)element.Value).Value.ToString(); break;
            case BsonType.String: value = ((BsonString)element.Value).Value; break;
        }
        return string.Format("{0}_{1}", element.Name, value.Replace(' ', '_'));
    }));
}