为什么我的TakeLimit不受TableQuery的尊重？

Question

我想用一个简单的TableQuery从我的Azure表中获取前n行.但是使用下面的代码,无论我对Take的限制如何,都会获取所有行.

我究竟做错了什么？

int entryLimit = 5;

var table = GetFromHelperFunc();

TableQuery<MyEntity> query = new TableQuery<MyEntity>()
    .Where(TableQuery.GenerateFilterCondition("PartitionKey", QueryComparisons.Equal, "MyPK"))
    .Take(entryLimit);

List<FeedEntry> entryList = new List<FeedEntry>();
TableQuerySegment<FeedEntry> currentSegment = null;

while (currentSegment == null || currentSegment.ContinuationToken != null)
{
    currentSegment = table.ExecuteQuerySegmented(query, this.EntryResolver, currentSegment != null ? currentSegment.ContinuationToken : null);
    entryList.AddRange(currentSegment.Results);
}


Trace.WriteLine(entryList.Count) // <-- Why does this exceed my limit?

Answer 1

存储SDK上的Take方法不像在LINQ中那样工作.想象一下,你做了这样的事情:

TableQuery<TableEntity> query = new TableQuery<TableEntity>()
                .Where(TableQuery.GenerateFilterCondition("PartitionKey", QueryComparisons.Equal, "temp"))
                .Take(5);
var result = table.ExecuteQuery(query);

当你开始迭代时,result你最初只会获得5个项目.但是在下面,如果你继续迭代result,SDK将继续查询表(并继续下一个'页面'的5项).

如果我的表中有5000个项目,则此代码将输出所有5000个项目(并且SDK下面将执行1000个请求并且每个请求获取5个项目):

TableQuery<TableEntity> query = new TableQuery<TableEntity>()
                .Where(TableQuery.GenerateFilterCondition("PartitionKey", QueryComparisons.Equal, "temp"))
                .Take(5);
var result = table.ExecuteQuery(query);
foreach (var item in result)
{
    Trace.WriteLine(item.RowKey);
}

以下代码将在1个请求中提取5个项目并停在那里:

TableQuery<TableEntity> query = new TableQuery<TableEntity>()
                .Where(TableQuery.GenerateFilterCondition("PartitionKey", QueryComparisons.Equal, "temp"))
                .Take(5);
var result = table.ExecuteQuery(query);
int index = 0;
foreach (var item in result)
{
    Console.WriteLine(item.RowKey);
    index++;
    if (index == 5)
        break;
}

实际上,Take()方法设置页面大小或"take count"(TableQuery上的TakeCount属性).但是如果你只想要5条记录,你仍然可以按时停止迭代.

在您的示例中,您应该修改while循环以在到达TakeCount时停止(通过调用Take设置):

while (entryList.Count < query.TakeCount && (currentSegment == null || currentSegment.ContinuationToken != null))
{
    currentSegment = table.ExecuteQuerySegmented(query, currentSegment != null ? currentSegment.ContinuationToken : null);
    entryList.AddRange(currentSegment.Results);
}

Answer 2

AFAIK Storage Client Library 2.0在Take实现中存在错误.它在版本2.0.4中修复.
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