I am working on .aspx page that uses a t-sql query that uses a multivalued input parameter (a set of labnames) using an array that would store all the labnames prior to running the query.
I have the following parameters for the query.
With c.Parameters
.Add(New SqlParameter("#sdate", sdate.text))
.Add(New SqlParameter("#edate", edate.text))
.Add(New SqlParameter("#labname", SqlDbType.Text)).Value = labnamesparam.ToString
End With
However, I still see that only one labname (3rd param in the order).
Any ideas on this?
For SQL 2008 your should use a TVP, as recommended by Marc.
For SQL 2005 there are several techniques like using XML or using a comma delimitted list. A comprehensive analysis of each technique is kept by Erland Sommarskog on hi page at http://www.sommarskog.se/arrays-in-sql-2005.html.
For SQL 2000 the options are fewer, and again Erland has a comprehensive discussion of each at Arrays and Lists in SQL Server (SQL 2000 and Earlier).
I highly recommend Erland's articles, they've been the reference on the subject for many years now.
You need to turn the contest of the array into a string. Here is a c# example, certainly not the only way to do it.
System.Text.StringBuilder k = new System.Text.StringBuilder();
foreach (string x in LABNAMES) {
k.Append(x);
k.Append(",");
}
.Add(New SqlParameter("#labname", SqlDbType.Text)).Value =k.ToString();
Your going to have to change your sql though you can't have a dynamic in clause like that. Old trick but not good practice is to turn the whole sql into a string and do an execute one it.
You might have to do a little bit more work in your stored procedure if you want to pass along an array of strings to it and perform a T-SQL "IN" operation.
This article has a very good example.
IF you use SQL Server 2008, you could use the "table-valued parameter" (TVP) feature.
Basically, in SQL Server 2008, you need to define a user-defined table type:
CREATE TYPE Customer AS
TABLE (id int, CustomerName nvarchar(50), postcode nvarchar(50))
and then use that in your stored procedure as a parameter:
CREATE Procedure AddCustomers(#customer Customer READONLY)
And then in your C# code, you'd create a DataTable variable of the same structure, and use that as the input parameter. That way, you can pass in any number of values, and any structure you like.
See these excellent blog posts for more information and extensive code samples:
Guy Burstein
Ben Hall
SQL-Team
Marc
Related
So far, I've been using classic ADO.NET model for database access. I have to tell you that I'm quite happy with it. But I have also been hearing much about Entity Framework recently so I thought I could give it a try. Actually the main reason which pushed me was the need to find a way to build the WHERE clause of my Stored Procedures. With the classic way I have to do either of the following:
Build the WHERE clause in the client side based on the user inputs and send it as a VARCHAR2 argument to the Stored Procedure, concatenate the WHERE clausewith the main part of the SQL and pass the whole string to EXECUTE_IMMEDIATE function. I personally hate to have to do so.
Inside the Stored Procedure construct lots and lots of SQL statements, which means I have to take all the possible combinations that WHERE clause might be composed of into account. This seems worse than the first case.
I know that EF has made it possible to use Stored Procedures as well. But will it be possible to build the WHERE part dynamically? Can EF rescue me somehow?
yes, you can use Dynamic queries in Linq.
Dynamic Query LIbrary
from scott gu example
var query = Northwind.Products.Where("Lastname LIKE "someValue%");
or some complex query
var query =
db.Customers.
Where("City = #0 and Orders.Count >= #1", "London", 10).
OrderBy("CompanyName").
Select("new(CompanyName as Name, Phone)");
or from this answer Where clause dynamically.
var pr = PredicateBuilder.False<User>();
foreach (var name in names)
{
pr = pr.Or(x => x.Name == name && x.Username == name);
}
return query.AsExpandable().Where(pr);
I've been tasked with creating an application that allows users the ability to enter data into a web form that will be saved and then eventually used to populate pdf form fields.
I'm having trouble trying to think of a good way to store the field values in a database as the forms will be dynamic (based on pdf fields).
In the app itself I will pass data around in a hash table (fieldname, fieldvalue) but I don't know the best way to convert the hash to db values.
I'm using MS SQL server 2000 and asp.net webforms. Has anyone worked on something similar?
Have you considered using a document database here? This is just the sort of problem they solve alot better than traditional RDBMS solutions. Personally, I'm a big fan of RavenDb. Another pretty decent option is CouchDb. I'd avoid MongoDb as it really isn't a safe place for data in it's current implementation.
Even if you can't use a document database, you can make SQL pretend to be one by setting up your tables to have some metadata in traditional columns with a payload field that is serialized XML or json. This will let you search on metadata while staying out of EAV-land. EAV-land is a horrible place to be.
UPDATE
I'm not sure if a good guide exists, but the concept is pretty simple. The basic idea is to break out the parts you want to query on into "normal" columns in a table -- this lets you query in standard manners. When you find the record(s) you want, you can then grab the CLOB and deserialize it as appropriate. In your case you would have a table that looked something like:
SurveyAnswers
Id INT IDENTITY
FormId INT
SubmittedBy VARCHAR(255)
SubmittedAt DATETIME
FormData TEXT
A few protips:
a) use a text based serialization routine. Gives you a fighting chance to fix data errors and really helps debugging.
b) For SQL 2000, you might want to consider breaking the CLOB (TEXT field holding your payload data) into a separate table. Its been a long time since I used SQL 2000, but my recollection is using TEXT columns did bad things to tables.
The solution for what you're describing is called Entity Attribute Value (EAV) and this model can be a royal pain to deal with. So you should limit as much as possible your usage of this.
For example are there fields that are almost always in the forms (First Name, Last Name, Email etc) then you should put them in a table as fields.
The reason for this is because if you don't somebody sooner or later is going to realize that they have these names and emails and ask you to build this query
SELECT
Fname.value fname,
LName.Value lname,
email.Value email,
....
FROM
form f
INNER JOIN formFields fname
ON f.FormId = ff.FormID
and AttributeName = 'fname'
INNER JOIN formFields lname
ON f.FormId = ff.FormID
and AttributeName = 'lname'
INNER JOIN formFields email
ON f.FormId = ff.FormID
and AttributeName = 'email'
....
when you could have written this
SELECT
common.fname,
common.lname,
common.email,
....
FROM
form f
INNER JOIN common c
on f.FormId = c.FormId
Also get off of SQL 2000 as soon as you can because you're going to really miss the UNPIVOT clause
Its also probably not a bad idea to look at previous SO EAV questions to give you an idea of problems that people have encountered in the past
I'd suggest mirroring the same structure:
Form
-----
form_id
User
created
FormField
-------
formField_id
form_id
name
value
I have list of words. I type in a word misspelled. Can I query the list using linq to get words that sounds like (soundex) the misspelled word?
I believe you can.
A quick google search came up with this link:
Code Snippet
from elt in SomeTable.AsEnumerable()
where SoundEx(elt.SomeWordsSoundExCode) == SoundEx("MyWord")
select elt;
If you want to use LINQ to SQL to query database, then you'll probably want to run the comparison on SQL side. You could use AsEnumerable, but then you'll need to implement the algorithm in C# and process the data in-memory.
I believe that LINQ to SQL doesn't provide any built-in method that would be translated to a call to the SOUNDEX function in SQL. However, you can add mapping for a user-defined SQL function (See for example this article). So, you could define your SQL function that performs the comparison and then write something like:
var db = new MyDatabaseContext();
var q = from w in db.Products
where db.SimilarSoundEx(w.Name, searchInput)
select w;
I just started learning LINQ to SQL, and so far I'm impressed with the easy of use and good performance.
I used to think that when doing LINQ queries like
from Customer in DB.Customers where Customer.Age > 30 select Customer
LINQ gets all customers from the database ("SELECT * FROM Customers"), moves them to the Customers array and then makes a search in that Array using .NET methods. This is very inefficient, what if there are hundreds of thousands of customers in the database? Making such big SELECT queries would kill the web application.
Now after experiencing how actually fast LINQ to SQL is, I start to suspect that when doing that query I just wrote, LINQ somehow converts it to a SQL Query string
SELECT * FROM Customers WHERE Age > 30
And only when necessary it will run the query.
So my question is: am I right? And when is the query actually run?
The reason why I'm asking is not only because I want to understand how it works in order to build good optimized applications, but because I came across the following problem.
I have 2 tables, one of them is Books, the other has information on how many books were sold on certain days. My goal is to select books that had at least 50 sales/day in past 10 days. It's done with this simple query:
from Book in DB.Books where (from Sale in DB.Sales where Sale.SalesAmount >= 50 && Sale.DateOfSale >= DateTime.Now.AddDays(-10) select Sale.BookID).Contains(Book.ID) select Book
The point is, I have to use the checking part in several queries and I decided to create an array with IDs of all popular books:
var popularBooksIDs = from Sale in DB.Sales where Sale.SalesAmount >= 50 && Sale.DateOfSale >= DateTime.Now.AddDays(-10) select Sale.BookID;
BUT when I try to do the query now:
from Book in DB.Books where popularBooksIDs.Contains(Book.ID) select Book
It doesn't work! That's why I think that we can't use thins kinds of shortcuts in LINQ to SQL queries, like we can't use them in real SQL. We have to create straightforward queries, am I right?
You are correct. LINQ to SQL does create the actual SQL to retrieve your results.
As for your shortcuts, there are ways to work around the limitations:
var popularBooksIds = DB.Sales
.Where(s => s.SalesAmount >= 50
&& s.DateOfSale >= DateTime.Now.AddDays(-10))
.Select(s => s.Id)
.ToList();
// Actually should work.
// Forces the table into memory and then uses LINQ to Objects for the query
var popularBooksSelect = DB.Books
.ToList()
.Where(b => popularBooksIds.Contains(b.Id));
Yes, query gets translated to a SQL string, and the underlying SQL can be different depending on what you are trying to do... so you have to be careful in that regard. Checkout a tool called linqpad, you can try your query in it and see the executing SQL.
Also, it runs when iterating through the collection or calling a method on it like ToList().
Entity framework or linq queries can be tricky sometimes. Sometimes you are surprised at the efficiency of the sql query generated and sometimes the query is so complicated and inefficient that you would smack your forehead.
Best idea is that if you have any suspicions about a query, run an sql profiler at the backend that would monitor all the queries coming in. That way you know exactly what is being passed on to the sql server and correct any inefficiencies if need be.
http://damieng.com/blog/2008/07/30/linq-to-sql-log-to-debug-window-file-memory-or-multiple-writers
This will help you to see what and when queries are being run. Also, Damiens blog is full of other linq to sql goodness.
You can generate an EXISTS clause by using the .Any method. I have had more success that way than trying to generate IN clauses, because it likes to retrieve all the data and pass it all back in as parameters to a query
In linq to sql, IQueryable expression fragments can be combined to create a single query, it will try to keep everything as an IQueryable for as long as it can, before you do something that cannot be expressed in SQL. When you call ToList you are directly asking it to resolve that query into an IEnumerable stored in memory.
In most cases you are better off not selecting the book ids in advance. Keep the fragment for popular books in a single place in the code and use it when necessary, to build on another query. An IQueryable is just an expression tree, which is resolved into SQL at some other point.
If you think your application will perform better by storing the popular books elsewhere (memcache or whatever), then you may consider pulling them out before hand, and checking against that later. This will mean each book id will be passed in as a sproc parameter and used in an IN clause.
I've got a search box that users can type terms into. I have a table setup with fulltext searching on a string column. Lets say a user types this: "word, office, microsoft" and clicks "search".
Is this the best way to deal with multiple search terms?
(pseudocode)
foreach (string searchWord in searchTerms){
select col1 from myTable where contains(fts_column, ‘searchWord’)
}
Is there a way of including the search terms in the sql and not iterating? I'm trying to reduce the amount of calls to the sql server.
FREETEXT might work for you. It will separate the string into individual words based on word boundaries (word-breaking). Then you'd only have a single SQL call.
MSDN -- FREETEXT
Well you could just build your SQL Query Dynamically...
string [] searchWords = searchTerm.Split(",");
string SQL = "SELECT col1 FROM myTable WHERE 1=2";
foreach (string word in searchWords)
{
SQL = string.Format("{0} OR contains(fts_column, '{1}')", SQL, word);
}
//EXEC SQL...
Obviously this comes with the usual warnings/disclaimers about SQL Injection etc... but the principal is that you would dynamically build up all your clauses and apply them in one query.
Depending on how your interacting with your DB, it might be feasible for you to pass the entire un-split search term into a SPROC and then split & build dynamic SQL inside the stored procedure.
You could do it similar to what you have there: just parse the search terms based on delimiter, and then make a call on each, joining the results together. Alternatively, you can do multiple CONTAINS:
SELECT Name FROM Products WHERE CONTAINS(Name, #Param1) OR CONTAINS(Name, #Param2) etc.
Maybe try both and see which is faster in your environment.
I use this class for Normalizing SQL Server Full-text Search Conditions