如何在Linq for DocumentDB中使用泛型創建多個/嵌套的SelectMany聯接

Question

我試圖將方法添加到文檔Db的通用存儲庫中。

我希望它產生看起來與此類似的SQL（但通用）：

SELECT VALUE c FROM c
JOIN versions IN c["versions"] 
JOIN groups IN versions["userGroups"] 
JOIN users IN groups["users"] 
WHERE c.type = "Approval" and users["userId"] = "xxx"

我已經嘗試過了...

public async Task<ListResult<TResult>> SelectManyAsync<TEntity1, TEntity2, TEntity3, TEntity4, TResult>(Expression<Func<TEntity1, bool>> condition01, Expression<Func<TEntity1, IEnumerable<TEntity2>>> condition02, Expression<Func<TEntity2, IEnumerable<TEntity3>>> condition03, Expression<Func<TEntity3, IEnumerable<TEntity4>>> condition04, Expression<Func<TEntity4, bool>> condition05) where TEntity1:class
        {
            var feedOptions = GetFeedOptions();

            var query = DocumentDbContext.Client.CreateDocumentQuery<TEntity1>(DocumentDbContext.DocumentCollection.DocumentsLink, feedOptions)
                .Where(condition01)
                .SelectMany(condition02)
                .SelectMany(condition03)
                .SelectMany(condition04)
                .Where(condition05)
                .AsDocumentQuery();

// .. removed code for brevity

}

結果是這樣的：

SELECT VALUE tmp FROM root 
JOIN tmp IN root["versions"] 
JOIN tmp IN tmp["userGroups"] 
WHERE (true AND (tmp["userId"] = "xxx"))

但是我得到了錯誤：

在FROM子句中多次指定了輸入集名稱或別名“ tmp”。

是否可以使用泛型創建類似的內容，以及如何為“ tmp”指定不同的值。 還是這不是正確的方法？

Answer 1

不知道是否該錯誤，此類查詢錯誤將無法工作。 您需要使用嵌套的selectMany。

以下示例應該起作用：

public async Task<IEnumerable<TRes>> Query<T, TRes>(
        string docCollection,
        string partitionKey,
        Func<IOrderedQueryable<T>, IQueryable<TRes>> func,
        string continuationToken = null)
    {
        var queryable =
            CosmosClient.CreateDocumentQuery<T>(
                CollectionUri(docCollection),
                new FeedOptions
                {
                    MaxItemCount = 100,
                    RequestContinuation = continuationToken,
                    EnableCrossPartitionQuery = false,
                    PartitionKey = new PartitionKey(partitionKey),
                    PopulateQueryMetrics = true,
                });

        return await func(queryable).AsDocumentQuery().ExecuteNextAsync<TRes>();
    }


await Query<Doc, string>("collection", "pk",
            (IOrderedQueryable<Doc> x) => x.SelectMany(p => p.Versions.SelectMany(d => d.UserGroups.SelectMany(k => k.Users.Select(u => u.Name)))));