C# - Efficient And Proper Linq Queries From Database
Nov 9, 2010
A sample linq query from MSDN: var expensiveInStockProducts = from p in products where p.UnitsInStock > 0 && p.UnitPrice > 3.00M select p; Does this query select EVERY column from the database table immediately, or does it return some sort of pointer that retieves the actual column data on demand? ie. If there are 50 columns in my table and I only use a single p.UnitsInStock in my actual code, then am I retrieving 50 times more data than I expected?
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Similar Messages:
Mar 17, 2010
I am having trouble with queries because they are not returning the data needed, and I am having trouble figuring out why because I only am testing with 2 records.First I want a query to return all records for one customer as follows:
[Code]....
There are two records with the customerID of 1, but it only returns one,next I try to return only one record, the AccountPrimary or customer_contacts.IsPrimary, but when I add " AND customer_contacts.IsPrimary = 'True' "at the end of my query it then returns both records, but only one IsPrimary = True and the Other = False. Is it backwards? I also tried another method and it returned 30 of the same record and I only have 2
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Oct 10, 2010
I've installed a Free TextBox editor to allow clients to do a write up about themselves and style it with HTML. Been reading about cross site script attacks (XSS) and want to make sure I'm correctly uploading the data collected with the Server.encode method.
Is this the right way to do it?:
[code]....
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Jan 11, 2011
When i see MVC Music store. They have used ADO.NET entity data model and used LINQ language to perform operation in DB.. Is there any way to use normal sql queries?
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Jul 31, 2010
How to convert SQL Queries to Linq.is their any tool available to convert SQL Queries to Linq
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Mar 18, 2010
I use LINQ-SQL as my DAL, I then have a project called DB which acts as my BLL. Various applications then access the BLL to read / write data from the SQL Database.
I have these methods in my BLL for one particular table:
public IEnumerable<SystemSalesTaxList> Get_SystemSalesTaxList()
{
return from s in db.SystemSalesTaxLists
select s;
}
public SystemSalesTaxList Get_SystemSalesTaxList(string strSalesTaxID)
{
return Get_SystemSalesTaxList().Where(s => s.SalesTaxID == strSalesTaxID).FirstOrDefault();
[Code].....
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Jul 27, 2010
Is it possible to combine these 2 linq queries ?
[Code]....
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Mar 18, 2011
I have this code in my controller:
public ActionResult Index()
{
MembershipUser currentUser = Membership.GetUser();
Guid UserId = (Guid)currentUser.ProviderUserKey;
using (var db = new MatchGamingEntities())
{
var MyAccount = from m in db.Accounts..........
I want to be able to do a join query between my two tables Accounts and BankTransactions. This is a one to many relationship, there can be multiple BankTransactions per Account. I want to query this and display the account information including all the bank statements that are associated with it. I did a join in order to get it, but I am having trouble handling the model. I keep getting this error:
LINQ to Entities does not recognize the method 'System.Collections.Generic.List1[MatchGaming.Models.BankTransaction] ToList[BankTransaction](System.Collections.Generic.IEnumerable1[MatchGaming.Models.BankTransaction])' method, and this method cannot be translated into a store expression.
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Oct 21, 2010
I am trying to delete record from table with proper mapping from linq to sql.There is an error stating that Rmove method not found and are u missing an assembly reference.
AdventureWorks db = new AdventureWorks("Integrated Security=sspi");
var query = from con in db.Contact
where con.LastName == "Klein"
select con;
foreach (Contact del in query)
{
db.Contact.Remove(del);//???Remove not working
}
db.SubmitChanges();
textBox1.Text = "Contact deleted.";
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Nov 7, 2010
I'm trying to do something that on the face of it is very simple.
If I have 5 text boxes, and 1 of them is blank, I want to exclude that textbox from the query, rather than searching for where a field is blank.
I've tried to do a bit of research into dynamic linq queries, but have come up empty handed, or what I've found doesn't seem to quite answer my question.
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Aug 20, 2010
I have my Linq query in which i need to find time difference(not days difference).
The field in database is datetime.
Dim ldtToday
As DateTime = TimeOfDay
Dim SR_RM_InnerJoin =
From SR
In lcntxRT60Entities.RtSReports _
Join RM
In lcntxRT60Entities.RtRMaster
On SR.RtRMaster.ReportID
Equals RM.ReportID _
Select SR, RM _
Where SR.TID = 1 _
And --(Check) SR.ReportDeliveryTime.Value.AddDays(1) < ldtToday
How can i check if the time field of the record is less than current time??
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Jan 16, 2011
I am new to databases and linq, so my problem may be considered trivial. I currently start all my db requests in each class with:
DataClassesDataContext db = new DataClassesDataContext()
Then I proceed to make whatever linq request I need within the method and carry on with the main application logic.
Now, two interesting queries:
1) I believe I have seen people wrapping db usage within 'using'. Such as:
using (DataClassesDataContext db = new DataClassesDataContext())
{
...
}
If this is correct, then doesn't it mean that my class can't use a member 'db' variable anymore, but rather those db requests need to be made within each function call? Also, what exactly would happen if I don't use 'using' within the calls?
2) Running my app with SQL Profiler enabled, I see lots of connections opening and closing. Does this means that each
DataClassesDataContext call makes a separate connection? It seems inefficient, so is the right way to actually make the DataClassesDataContext object a static within each class being used?
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Nov 2, 2010
I am creating entries in a contract table using linq to sql.
One column needs to conditionally be assigned an application number from a range of values.
I'd like to simply increment the max existing value, however it is a multi-user application and I'm concerned about multiple contracts receiving the same app number if they happen too close together.
Is there a way to either force the entire thing to use the same transaction, or to execute both during the same submit?
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Dec 17, 2010
how to improve the application performance while writing LINQ Queries ?Like the optimization techniques.
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Dec 29, 2010
I've got the following LINQ query to my IQueryable service
Dim eventcount = EventService.QueryEvents().Count
Dim eventlist = EventService.QueryEvents().Skip((page - 1) * 5).Take(5).ToList
But I'm wondering if there's a way to do this without making two calls to the database?
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Nov 10, 2010
i want to get masterized....in MVC
finding books and links for mvc..and learning linq queries
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Mar 6, 2011
Is there a way to cap the number of records returned when an .Include() method is called on an ObjectQuery<>? Basically, if one of my entities is in a one-to-many relationship, such as a Band entity to a list of Fan entities (where a band can have any number of fans), how can I limit the number of fans returned?
In the example: var band = ctx.Bands.Include("Fans").SingleOrDefault(b => b.BandId == someBandId);
If I use the Include, it will return all fans. How can I query that Fans navigation property to return only a subset or max?
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Aug 8, 2010
I've got a linq to sql query that pulls data from 2 different tables and contains an or statement:
[Code]....
The problem I've got is that some queries match both sides of the or statement so it returns the same record twice.
How can I eliminate these duplicates quickly and easily?
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Jun 24, 2010
I am wondering what the most efficient method is for retreiving a single cell of data from my database. I have a price table in my DB that I just need to look up one price at a time. Currently I load a dataset and call ds.tables(0).rows(0).item(0) for the value. I just want to make sure this is the best way do this.
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Jan 16, 2011
Im new to database design and I would like to know what is the best way to design a tagging system such as the one that stackoverflow has?
I found multiple ways to design such a system on the web, but not sure which one is the most optimal.
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May 25, 2010
I am working on asp.net 3.5 and in MVC using Linq to SQL classes. In my MVC project i am calling stored procedure using linq to sql that conatin query joining two tables.Below is my code in Partial class
[
Function(Name="dbo.GetUserWiseThreadDetail_SP")]
[ResultType(typeof(Thread))]
[ResultType(typeof(Reply))]
public
IMultipleResults GetUserWiseThreadDetail_SP([Parameter(DbType="VarChar(30)")]
string userID)
{
ExecuteResult result = this.ExecuteMethodCall(this,
(MethodInfo)(MethodInfo.GetCurrentMethod())), userID);
return ((IMultipleResults)(result.ReturnValue));
}
In one of the controller i have made one more class
public class
MypostIndexData
{
public
IEnumerable<Thread> Thrds {
get;
set; }
public
IEnumerable<Reply> Repls {
get;
set; }
public MypostIndexData(IEnumerable<Thread>
thrds,IEnumerable<Reply> repls)
{
this.Thrds=thrds;this.Repls=repls;
}
}
finally coding of controller action method
ForumDataContext pmforum = new
PMForumDataContext();
public
ActionResult MyPosts(string userId)
{
IEnumerable<Thread>thrds;
IEnumerable<Reply>repls;
IMultipleResults result = pmforum.GetUserWiseThreadDetail_SP(userId); (this satement doesnot give any result,if i execute stored proc in
sql it give the results)
thrds = result.GetResult<Thread>();
List<Thread> thrdlist =
new
List<Thread>(thrds);
repls = result.GetResult<Reply>();
List<Reply> replylist;
if (repls !=
null)
{
replylist = new
List<Reply>(repls);
}
return View(new
MypostIndexData(thrds,repls));
I am unable to understand why i am not getting any results?
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Feb 25, 2010
Is there a way to combine the LINQ queries together and have access to both of the results independently?
[Code]....
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Aug 31, 2010
Among methods: static variables, viewstate, session and cache for avoiding on loading repeatedly and less making queries to the database. What do you think the best method of the 4 above? I Think Cache is the best one? Or any other methods better in Asp.net 3.5 or higher?
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Aug 17, 2010
I'm after some thoughts on how people go about calculating database load for the purposes of capacity planning. I haven't put this on Server Fault because the question is related to measuring just the application rather than defining the infrastructure. In this case, it's someone else's job to worry about that bit! I'm aware there are a huge number of variables here but I'm interested in how others go about getting a sense of rough order of magnitude. This is simply a costing exercise early in a project lifecycle before any specific design has been created so not a lot of info to go on at this stage.
The question I've had put forward from the infrastructure folks is "how many simultaneous users". Let's not debate the rationale of seeking only this one figure; it's just what's been asked for in this case! This is a web front end, SQL Server backend with a fairly fixed, easily quantifiable audience. To nail this down to actual simultaneous requests in a very rough fashion, the way I see it, it comes down to increasingly granular units of measurement:
Total audience
Simultaneous sessions
Simultaneous requests
Simultaneous DB queries
This doesn't account for factors such as web app caching, partial page requests, record volume etc and there's some creative license needed to define frequency of requests per user and number of DB hits and execution time but it seems like a reasonable starting point. I'm also conscious of the need to scale for peak load but that's something else that can be plugged into the simultaneous sessions if required. This is admittedly very basic and I'm sure there's more comprehensive guidance out there. If anyone can share their approach to this exercise or point me towards other resources that might make the process a little less ad hoc
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Aug 30, 2010
I need to do some performance testing for an ASP.NET MVC application and specifically want to measure how many database queries each HTTP request results in. The data access layer is using LINQ-to-SQL. I'd like to be able to automate the tests so am looking for a good way to be able to do a before and after count of the number of SQL queries. The possibilities I can think of are: A performance monitor counter for the ASP.NET process, A system table in the MSSQL database that can be queried before and after each page request, A property somewhere in the System.Data.SQLClient namespace that tracks the number of queries executed by the process. Has anyone done this before and can perhaps point my down the right path?
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