UpdateManyAsync和update在Mongo shell中的工作方式相同。因此，您可以指定过滤条件和更新操作，它将影响多个文档。例如，要递增所有a字段，其中a大于10，您可以使用以下方法：

var builder = Builders<SampleClass>.Update;
await myCollection.UpdateManyAsync(x => x.a > 10, builder.Inc(x => x.a, 1));

我猜你想替换多个文档。这可以用bulkWrite方法来实现。如果你需要C#中的泛型方法，那么你可以引入某种标记接口来构建替换操作的过滤器部分：

public interface IMongoIdentity
{
    ObjectId Id { get; set; }
}

然后，您可以向类中添加泛型constain，并在.NET中使用BuikWrite，如下所示：

class YourRepository<T> where T : IMongoIdentity
{
    IMongoCollection<T> collection;

    public async Task UpdateManyAsync(IEnumerable<T> entities)
    {
        var updates = new List<WriteModel<T>>();
        var filterBuilder = Builders<T>.Filter;

        foreach (var doc in entities)
        {
            var filter = filterBuilder.Where(x => x.Id == doc.Id);
            updates.Add(new ReplaceOneModel<T>(filter, doc));
        }

        await collection.BulkWriteAsync(updates);
    }
}

正如@mickl的回答，您不能使用x=〉x.Id，因为它是一个通用用法，如下所示：

public async Task<string> UpdateManyAsync(IEnumerable<T> entities)
{ 
     var updates = new List<WriteModel<T>>();
     var filterBuilder = Builders<T>.Filter;

     foreach (var doc in entities)
     {
          foreach (PropertyInfo prop in typeof(T).GetProperties())
          {
              if (prop.Name == "Id")
              {
                  var filter = filterBuilder.Eq(prop.Name, prop.GetValue(doc));
                  updates.Add(new ReplaceOneModel<T>(filter, doc));
                  break;
              }
          }
     }
     BulkWriteResult result = await _collection.BulkWriteAsync(updates);
     return result.ModifiedCount.ToString();
}

或者按照Bson属性：

public async Task UpdateManyAsync(IEnumerable<TEntity> objs, CancellationToken cancellationToken = default) 
{
var updates = new List<WriteModel<TEntity>>();
var filterBuilder = Builders<TEntity>.Filter;

foreach (var obj in objs)
{
    foreach (var prop in typeof(TEntity).GetProperties())
    {
        object[] attrs = prop.GetCustomAttributes(true);
        foreach (object attr in attrs)
        {
            var bsonId = attr as BsonIdAttribute;
            if (bsonId != null)
            {
                var filter = filterBuilder.Eq(prop.Name, prop.GetValue(obj));
                updates.Add(new ReplaceOneModel<TEntity>(filter, obj));
                break;
            }
        }
    }
}

await _dbCollection.BulkWriteAsync(updates, null, cancellationToken);

}