I am working with an old app that is using linq to sql.
I have a work around for the problem below but I am wondering if anyone has run into this and knows what the root cause might be.
I have a linq statement which has a number of joins in it. I don't think the statement itself is the problem since it has been working for months without the issue I'm about to describe (blank fields have been part of the data since the start). When I log the sql generated by the context from the linq statement and then run that sql in sql server managment studio, I have one column which has some fields that are blank. By blank I mean string.empty not NULL. None of the rows are NULL as verified by adding a 'where' clause that filters out NULLs.
However when that statement then gets mapped to entities by the linq2sql framework, some of the entities have that field set to string.empty some are set to NULL. I have verified that those which are set to NULL on the c# side are in fact BLANK on the sql server side.
I have a loop that goes over the results and sets all NULLs to string.empty after the query is returned as a list, but it would be nice if there was a more elegant fix for this.
Related
I'm working on several reports for SSRS written in MySQL via ODBC Adapter. For some reason, Stored Procedures only return a single row of data instead of an expected set of data.
Below is the same stored procedure when ran on an SQL Editor:
And below is the stored procedure's execution result when SSRS tries to run it (both on Query Designer and Report Viewer):
I have also set parameters properly as far as i can tell:
so i wasn't able to find an exact answer as to why this happens on SSRS with MySQL via ODBC. What i was able to find was a workaround:
by executing the command as an Expression rather than as a raw query via the Query Editor:
Now the only caveat for this is that the DataSet Fields wouldn't be automatically generated, and that you have to plot them all manually. A good workaround for this is to first run a blank/null query with only the column names (i.e.: SELECT NULL 'column_name_1', NULL 'column_name_2') then later change the query source to Expression. The good thing about using expression is that you only need minor knowledge about how it works and it reduces the confusion with ODBC '?' Parameters.
Cheers!
This question is quite open ended. Maybe it doesn't belong here, so sorry in advance if that's the case.
I'm using SQL in a real project for the first time, and I'm having some issues. I'm also using php and javascript.
In the web app I'm currently writing, i do a lot of SQL query to my MySQL database. Each one of these query do a different thing, on different tables, etc.
At the moment, I'm doing the following : each time i do a query in the client side code, I'm passing a parameter I defined myself to the server.
On the server, I wrote a switch on this parameter. So it looks like this :
if (parameter == 1)
/*Query 1*/
else if (parameter == 2)
/*Query 2*/
etc.
It's not very convenient. However, if i use a function writing a SQL query by taking parameters from the client, it would be subject to SQL injection.
So to sum it up : how do i create a SQL query in the most "modular" way possible and still avoid SQL injection ?
I already know about prepared statement, but if i get it right, i can't write a full SQL query with only prepared statement.
I am currently in the process of moving all my Access databases to a MySQL server. I have some pretty big queries I would like to convert into sql direct.
The only thing is that in those queries I am using the content of a textbox in my form :
IIf(IsNull([Formulaires]![DialogueMAJDossier]![FiltreTypeEntree]),[TypeDossier],[Formulaires]![DialogueMAJDossier]![FiltreTypeEntree])
(Excuse me for all the names being in french)
I know that when I convert it to MySQL syntax, it should give something like this :
IFNULL(`Formulaires`.`DialogueMAJDossier`.`FiltreTypeEntree`, `TypeDossier`)
But I have no idea how to account for the text box value in my query.
Any help will be gladly appreciated
Pass-Through queries cannot have parameters, so you'll have to use a workaround.
Option 1:
Save the SQL with "variables" in a template table, e.g. SELECT foo, {FiltreTypeEntree} FROM bar.
Then before executing the Pass-Through query, read the template SQL, Replace() the variable with the result of your IIf expression, and set the .SQL property of the query with the final string.
Option 2:
Create a "Variables" table in MySql. Fill its fields via code, and have your Pass-Through query join this table to get the variable values.
In a multi-user scenario, you'd have to introduce some kind of session management for Option 2, so I'd go with (1) in this case.
I have a very weird situation here. During development I discovered that one of my tables got more and more empty rows (the Id field is auto-incremented and was set). No insert statement was run from my code.
I use SQL Manager 2010 Lite for MySQL to inspect the data, and it turns out that when I Execute the select statement from there, the empty row gets added.
Has anyone else experienced this? All i do is right click the table, select 'Script to NEW SQL Editor' and Select. When I press Execute, the row gets added.
Not really an answer - I'm using phpmyadmin myself - but you could try setting one of the columns to not null? Just to see what happens, and what kind of error message you get? And you could also check to see if there are any stored procedures that could cause this.
Normally I would post this in a comment, but I don't have enough rep to do that yet, sorry...
When you run Linq to Sql or Linq to Entites to get a list of records it runs query to select all fields from a table. Is it an efficient solution. Lets say: I run this LINQ
dim lstCustomers = from c in db.Customers select c
it run query to get all fields from a table whether i need all fields or not. I am using asp.net with MVC so should i write this query in view (where i only need CustomerID and name)
dim lstCustomers = from c in db.Customers _
select new Customer with { c.CustomerID, c.Name }
If i have to use 2nd query then whats the advantage of LINQ and Entity Framework. This thing i can do with SQL query (with different syntax)
Anyone can help?
First of all, LINQ queries are evaluated lazily. That means that single line doesn't do anything but itself, so I assume you actually iterate the results with For Each.
The answer to your first question is yes, all fields are retrieved from the database with the first statement.
Yes, but in order to use SQL directly, you'll have to manually create entity classes, manually retrieve data using SqlDataReader or something to achieve the level of abstraction LINQ provides in that line. That's lots of more work on your behalf. With LINQ to SQL, you don't even need to explicitly write code to open a connection to database.
actuly linq have different sets of advantages over writing normal writing sql queries:
if you wrote sql queries then overloaded steps:
1. you need a sql connection class
2. you need a sql command or sqldataadapter.
3.then you need a container like datatable and dataset.
so while using linq you dont need all those steps. just write the queries as you wrote above.
also incase you wrote something incorrect in your sqlquery then there is no compile time error. error only generates when you execute the query during runtime.
but unlike sql queries, linq provides you the compile time error.
also linq is best of strongly type collections.