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POLINQ to entities execution order/timing question
 

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  1. POLINQ to entities execution order/timing question
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    <p>I have two long queries, each of type "typeViewRequest"</p> <pre><code> results1 = ..... (timeout) results2=..... (timeout) </code></pre> <p>Now.....</p> <p>Case 1-----------------------------------------------------------------------------</p> <p>If I do</p> <pre><code> results1 = ..... .Take(countRecordsToShow/2) results2 = ..... .Take(countRecordsToShow/2) </code></pre> <p>and then I say</p> <pre><code> results = results1.Union&lt;typeViewRequest&gt;(results2); </code></pre> <p>it works fine. The grid, using paging, shows the countRecordsToShow records, no problem here.</p> <p>Case 2-----------------------------------------------------------------------------</p> <p>If I do</p> <pre><code> results1 = ..... results2 = ..... </code></pre> <p>and then I say</p> <pre><code> results = results1.Union&lt;typeViewRequest&gt;(results2).Take(countRecordsToShow) </code></pre> <p>then I have a timeout. Why ? Because my gridview, obviously, needs to get the count of records, to set its paging. My SelectCountMethod, called getPreviousRequestsSelectCount, simply says </p> <pre><code>public int getPreviousRequestsCountFromDB(String name, DateTime dtStart, DateTime dtEnd, ReportedBy_Filter reportedBy, Status_Filter status, ReportType_Filter type, int countRecordsToShow, int userID) { return getPreviousRequests(companyNameLike: name, dtStart: dtStart, dtEnd: dtEnd, reportedBy: reportedBy, status: status, type: type, sortExpression: null, userID: userID, countRecordsToShow: countRecordsToShow).Count(); } </code></pre> <p>Inside getPreviousRequests, in Case1, TAKE is applied (as described in "case 2"):</p> <pre><code>results = results1.Union&lt;typeViewRequest&gt;(results2).Take(countRecordsToShow) </code></pre> <p>while countRecordsToShow is only 20, but it times out ! I cache that number until the filtering criteria changes, yes, but still... :-(( </p> <p>Additional problem: I also have some filtering to do. This filtering should happen on BOTH branches, like so:</p> <pre><code> results1 = ..... Where (something1) results2 = ..... .Where (something2) </code></pre> <p>but if I say, like in case 1,</p> <pre><code> results1 = ..... Where (something1).Take(countRecordsToShow/2) results2 = ..... .Where (something2).Take(countRecordsToShow/2) </code></pre> <p>this will CUT my filtered datasets, I'm afraid - let's say that countRecordsToShow = 20. If results1 (filtered by something1) had, say, 15 records, I would take only 10. If results2 (filtered by something2) had, say, 5 records, I would take 5. Then the UNION would have 15 instead of 20 records.</p> <p>Normally I should do this, like in Case2:</p> <pre><code> results1 = ..... Where (something1) results2 = ..... .Where (something2) </code></pre> <p>AND then say </p> <pre><code>results = results1.Union&lt;typeViewRequest&gt;(results2).Take(countRecordsToShow) </code></pre> <p>If the filtered results1.Union(results2) had 25 records but countRecordsToShow were 20, then so be it. I would just say that the dataset is not complete, and additional filtering is necessary.</p> <p>But since I have to trim the dataset BEFORE the UNION, this will affect my filtering BADLY !</p> <p>I expected that the resulted query will first pull each branch, then execute the UNION, then filter, and then trim, right at the end.</p> <p>Well, apparently if I don't trim each branch before doing anything else, I get a timeout.</p> <p>How does this all work ? I'm VERY confused. I cannot even use a COUNT to find out how many records I should expect, and to behave in consequence, because COUNT enumerates the dataset, thus giving me a timeout.</p> <p>What are my options, please ? (short of creating sprocs, which I am not allowed to do). Right now the only "solution" I have found is case1 - to apply a TAKE clause to each of the branches, BEFORE the Union, but, as I've mentioned, that would be wrong with regard to filtering. </p> <p>What am I doing wrong here ? Do I really need to go with the "logically handicapped" case1 ? Please help !</p> <p>Thank you</p> <p>Alex</p> <p>Note: </p> <p>I have tested this: If after executing the line</p> <pre><code>results = results1.Union&lt;typeViewRequest&gt;(results2).Take(20) </code></pre> <p>I try to check </p> <pre><code>results.count() </code></pre> <p>in the immediate window, it times out ! Does it not see that it has a .Take(20) clause ? Why does it have to enumerate ALL the records first ??? I should enumerate up to the limit, 20, and then stop. Apparently it enumerates all the way to about 250.000, and then trims the resultset to 20.</p> <p>Note: I read here: <a href="http://www.codeproject.com/KB/linq/linq_in_dept.aspx" rel="nofollow">Exploring LINQ Query Operators and Differed Execution Plan </a> that both TAKE and UNION are deffered. So then.... why is not TAKE integrated into the query, but applied AFTER the fact ?</p>
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