How to update many documents using UpdateManyAsync - mongodb

Question

I have the following method to update a document in MongoDB:
public async Task UpdateAsync(T entity)
{
await _collection.ReplaceOneAsync(filter => filter.Id == entity.Id, entity);
}
Which works fine - I was just wondering if anybody has an example of how the UpdateManyAsync function works:
public async Task UpdateManyAsync(IEnumerable<T> entities)
{
await _collection.UpdateManyAsync(); // What are the parameters here
}
Any advice is appreciated!

Answer 1

UpdateManyAsync works the same way as update with multi: true in Mongo shell. So you can specify filtering condition and update operation and it will affect multiple documents. For instance to increment all a fields where a is greater than 10 you can use this method:
var builder = Builders<SampleClass>.Update;
await myCollection.UpdateManyAsync(x => x.a > 10, builder.Inc(x => x.a, 1));
I guess you'd like to replace multiple documents. That can be achieved using bulkWrite method. If you need generic method in C# then you can introduce some kind of marker interface to build filter part of replace operation:
public interface IMongoIdentity
{
ObjectId Id { get; set; }
}
Then you can add generic constaint to your class and use BuikWrite in .NET like below:
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);
}
}

Answer 2

As #mickl answer, you can not use x=> x.Id because it is a Generic
Use as below:
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();
}

Answer 3

Or you go by Bson attribute:
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);
}