Repository that support query by partition key without change interface

Question

I am developing an application that using IDocumentClient to perform query to CosmosDB. My GenericRepository support for query by Id and Predicate.

I am in trouble when change Database from SqlServer to CosmosDb, in CosmosDb, we have partition key. And I have no idea how to implement repository that support query by partition key without change interface to pass partition key as a argument.

public interface IRepository<T>
{
    //I can handle this one by adding value of partition key to id and split it by ":"
    Task<T> FindByIdAsync(string id);

    // I am stuck here!!!
    Task<T> FindByPredicateAsync(Expression<Func<T, bool>> predicate);
}

My implementation

public class Repository<T> : IRepository<T>
{
    private readonly IDocumentClient _documentClient;

    private readonly string _databaseId;
    private readonly string _collectionId;

    public Repository(IDocumentClient documentClient, string databaseId, string collectionId)
    {
        _documentClient = documentClient;

        _databaseId = databaseId;
        _collectionId = collectionId;
    }

    public async Task<T> FindByIdAsync(string id)
    {
        var documentUri = UriFactory.CreateDocumentUri(_databaseId, _collectionId, id);

        try
        {
            var result = await _documentClient.ReadDocumentAsync<TDocument>(documentUri, new RequestOptions
            {
                PartitionKey = ParsePartitionKey(documentId)
            });

            return result.Document;
        }
        catch (DocumentClientException e)
        {
            if (e.StatusCode == HttpStatusCode.NotFound)
            {
                throw new EntityNotFoundException();
            }

            throw;
        }
    }
    
    public async Task<T> FindByPredicateAsync(Expression<Func<T, bool>> predicate)
    {
         //Need to query CosmosDb with partition key here!
    }

    private PartitionKey ParsePartitionKey(string entityId) => new PartitionKey(entityId.Split(':')[0]);
}

Any help is greatly appreciated, thanks.

Answer 1

I've found out the solution to keep your repository independent of database(I am using v3 SDK for example). Just separated current interface into 2 parts:

public interface IRepository<T>
{
    Task<T> FindItemByDocumentIdAsync(string documentId);

    
    Task<IEnumerable<T>> FindItemsBySqlTextAsync(string sqlQuery);

    Task<IEnumerable<T>> FindAll(Expression<Func<T, bool>> predicate = null);
}

public interface IPartitionSetter<T>
{
    string PartititonKeyValue { get; }

    void SetPartitionKey<T>(string partitionKey);
}//using factory method or DI framework to create same instance for IRepository<T> and IPartitionSetter<T> in a http request

Implementation:

public class Repository<T> : IRepository<T>, IPartitionSetter<T>
{
    //other implementation

    public async Task<IEnumerable<T>> FindAll(Expression<Func<T, bool>> predicate = null)
    {
        var result = new List<T>();
        var queryOptions = new QueryRequestOptions
        {
            MaxConcurrency = -1,
            PartitionKey = ParsePartitionKey()
        };

        IQueryable<T> query = _container.GetItemLinqQueryable<T>(requestOptions: queryOptions);

        if (predicate != null)
        {
            query = query.Where(predicate);
        }

        var setIterator = query.ToFeedIterator();
        while (setIterator.HasMoreResults)
        {
            var executer = await setIterator.ReadNextAsync();

            result.AddRange(executer.Resource);
        }

        return result;
    }

    private string _partitionKey;

    public string PartititonKeyValue => _partitionKey;

    private PartitionKey? ParsePartitionKey()
    {
        if (_partitionKey == null)
            return null;
        else if (_partitionKey == string.Empty)
            return PartitionKey.None;//for query documents with partition key is empty
        else
            return new PartitionKey(_partitionKey);
    }

    public void SetPartitionKey<T>(string partitionKey)
    {
        _partitionKey = partitionKey;
    }
}

You will need to inject IPartitionSetter<T> and call SetPartitionKey before execute query to apply partition key here.