为什么我的TakeLimit由TableQuery兑现？ [英] Why isn't my TakeLimit honored by TableQuery?

问题描述

我想取顶部的 N 的从我的Azure表行用一个简单的TableQuery。但与下面的code，所有行，而不管端来一我的极限在服用。

我在做什么错了？

  INT entryLimit = 5;变种表= GetFromHelperFunc（）;TableQuery＆LT;＆myEntity所GT;查询=新TableQuery＆LT;＆myEntity所GT;（）
    。凡（TableQuery.GenerateFilterCondition（PartitionKey，QueryComparisons.EqualMyPK））
    。取（entryLimit）;清单＆LT; FeedEntry＆GT; entryList =新的List＆LT; FeedEntry＆GT;（）;
TableQuerySegment＆LT; FeedEntry＆GT; currentSegment = NULL;而（currentSegment == NULL || currentSegment.ContinuationToken！= NULL）
{
    currentSegment = table.ExecuteQuerySegmented（！？查询，this.EntryResolver，currentSegment = NULL currentSegment.ContinuationToken：NULL）;
    entryList.AddRange（currentSegment.Results）;
}
Trace.WriteLine（entryList.Count）//＆LT;  - 为什么这超出我的极限？
 

解决方案

在存储SDK取方法并不像它会在LINQ工作。想象一下，你做这样的事情：

  TableQuery＆LT; TableEntity＆GT;查询=新TableQuery＆LT; TableEntity＆GT;（）
                。凡（TableQuery.GenerateFilterCondition（PartitionKey，QueryComparisons.Equal，TEMP））
                。取（5）;
VAR的结果= table.ExecuteQuery（查询）;
 

当你开始遍历结果您最初将只得到5个项目。但骨子里，如果你一直遍历结果，SDK将保留查询表（并继续以5个项目的下一个页面'）

如果我在我的表5000项，这code将输出所有5000项（和SDK会做1000个请求，并获取每个请求的5项下）：

  TableQuery＆LT; TableEntity＆GT;查询=新TableQuery＆LT; TableEntity＆GT;（）
                。凡（TableQuery.GenerateFilterCondition（PartitionKey，QueryComparisons.Equal，TEMP））
                。取（5）;
VAR的结果= table.ExecuteQuery（查询）;
的foreach（在结果VAR项）
{
    Trace.WriteLine（item.RowKey）;
}
 

以下code将获取1请求正好5个项目，并停在那里：

  TableQuery＆LT; TableEntity＆GT;查询=新TableQuery＆LT; TableEntity＆GT;（）
                。凡（TableQuery.GenerateFilterCondition（PartitionKey，QueryComparisons.Equal，TEMP））
                。取（5）;
VAR的结果= table.ExecuteQuery（查询）;
INT索引= 0;
的foreach（在结果VAR项）
{
    Console.WriteLine（item.RowKey）;
    指数++;
    如果（指数== 5）
        打破;
}
 

其实，在以（）方式设置页面大小或走数（<一href=\"http://msdn.microsoft.com/en-us/library/microsoft.windowsazure.storage.table.tablequery.takecount.aspx\">TakeCount财产上TableQuery）。但它仍然是由你来停止迭代时间，如果你只想要5条记录。

在你的榜样，您应该修改while循环停止到达TakeCount（这可以通过调用采取设置）时：

 而（entryList.Count＆LT; query.TakeCount＆放大器;＆安培;！（currentSegment == NULL || currentSegment.ContinuationToken = NULL））
{
    currentSegment = table.ExecuteQuerySegmented（查询，currentSegment = NULL currentSegment.ContinuationToken：！NULL）;
    entryList.AddRange（currentSegment.Results）;
}
 

I'd like to fetch top n rows from my Azure Table with a simple TableQuery. But with the code below, all rows are fetched regardless of my limit with the Take.

What am I doing wrong?

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?

解决方案

The Take method on the storage SDK doesn't work like it would in LINQ. Imagine you do something like this:

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

When you start iterating over result you'll initially get only 5 items. But underneath, if you keep iterating over the result, the SDK will keep querying the table (and proceed to the next 'page' of 5 items).

If I have 5000 items in my table, this code will output all 5000 items (and underneath the SDK will do 1000 requests and fetch 5 items per request):

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);
}

The following code will fetch exactly 5 items in 1 request and stop there:

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;
}

Actually, the Take() method sets the page size or the "take count" (TakeCount property on TableQuery). But it's still up to you to stop iterating on time if you only want 5 records.

In your example, you should modify the while loop to stop when reaching the TakeCount (which you set by calling Take):

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

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