Is anyone heard of any tool writing LINQ queries and converting them to SQL queries?
I mostly need this because I am a .NET developer and I'm weak in this section of SQL queries where sometimes I need them.
Thank you.
Have you tried using LINQPad? That lets you see the SQL generated when it runs the query - and of course it's easy to experiment with to get the LINQ query right to start with :)
If you write your query against a linq-to-sql datacontext, you can get the query text out like this:
CustomDataContext dc = new CustomDataContext(); //your DataContext here.
IQueryable<Customer> customerQuery = GetQuery(dc); //your query constructed here.
Console.WriteLine(dc.GetCommand(customerQuery).CommandText);
Use sql profiler to get the sql as it is executed against the sql database.
Related
I Just want to make sure I understand this correctly...
search is an object that contains a querystring.
Repo.Query returns an ObjectQuery<T>.
From my understanding the chained linq statements will filter the results after entity framework has returned all the rows satisfying the query. So really ALL the rows are being returned and THEN filtered in memory. So we are returning a bunch of data that we don't really want. There's about 10k rows being returned so this is kind of important. Just like to get my confusion cleared up.
var searchQuery = Repo.Query(search)
.Where(entity =>
entity.Prop1.ToUpper().Equals(prop1.ToUpper()) &&
entity.Prop2.ToUpper().Equals(prop2.ToUpper()))
.OrderBy(entity => Repo.SortExpression ?? entity.prop1);
Your Repo.Query(string query) function should return IQueryable<T>.
Then you can filter and order without getting all rows first.
IQueryable(Of T) Interface
hope this helps
If this is to SQL, this will most likely create a SQL query and filter on the server and not in memory.
As a matter of fact, the statement above wouldn't actually do anything.
It's only when you iterate over it that the query will be executed. This is why certain providers (like the EF to SQL one) can collapse expression trees into a SQL query.
Easiest way to check is to use LINQPAD or the SQL Profiler to see what query is actually is executed.
Looking at Dynamic Linq, it's possible to use strings to define the key parts of the query. My question is, is it possible to pass the entire query in as a string?
ie: var foo = "from..."
LINQ stands for "Language INtegrated Queries" - it's compiled with the rest of the code, not parsed on the run. You can use Microsoft.CSharp.CSharpCodeProvider to compile your query on the run - but you will have to know in advance what local objects you want to send to the query.
That's not possible in dynamic LINQ -- dynamic LINQ only replaces specific pieces of the query. You can use ExecuteQuery on the data context in LINQ to SQL or SqlQuery on a DbSet<T>, though, to execute specific SQL commands.
I have to Pull all customers whose ids are in the list
I have a list of CustomerID`s
List custidlist=new List{1,2,3....etc.}();
i have to write a linq query to get all customers whose id`s are in the above list
custidlist.
var customers=db.Customers.Where(c=> custidlist.Contains(c.customerid));
Using Contains is not good in performance issue.
Can we use COMPARE OPERATOR LIKE THIS
var customers=db.Customers.Where(c=> custidlist.Compare(c.customerid)); ????
I Heard Compare is best for Performance
Since this is Linq to SQL / Entities your Linq Contains query will be translated to a SQL statement roughly like:
select * from Customers where customerId in (1,2,3)
Not only is your other suggestion not supported, but also you cannot do any better than this SQL performance wise.
When you write a Contains query in Linq to SQL it iwll be fired as an in query in SQL and running your query on the databse should be the fastest..
one caveats to this though is to remember in query might have a limit on the number of entities I think its around 2000+ in sql server and the way around this would be to batch your query.
Hi Experts
I have a special question About dynamic Linq to Sql.
Consider we want to search in a table according two fields*(LetterNo(string) and LetterDate(Datetime))*
.OK the problem is user can enter on of that fields or even both.
I searched in the internet and found "Linq.Dynamic" library in ScottGu weblog.but in that library if we want to use SqlParameter in exported command we should use #0 and param for that.problem is I don't know how many fields user entered.
I want use one query for that and no external tool like "Linq Kit PredicateBuilder".
If I create my query string Manually(and execute using ExecuteCommand) then I will abdicate SqlParameter and risk of Sql Injenction growing up.
How Can do that?
thanks
I suspect you are wanting to do something like the following:
IQueryable<Letter> query = context.Letters;
if (!string.IsNullOrEmpty(LetterNo))
query = query.Where(letter => letter.LetterNo == LetterNo);
If (LetterDate.HasValue)
query = query.Where(letter => letter.LetterDate == LetterDate);
When you execute query, it will combine the necessary expressions and issue a single query to the database based on the user's input.
I thought that the purpose of using Linq2Nibernate was to return IQueryable and build up an expression tree. I am not sure if this is correct or not.
Why would anyone use Linq2Nibernate if they are not going to return IQueryable?
What else would it be used for?
I would love some more input on this topic
Linq For Nhibernate
I'm planning to use NHibernate.Linq to replace my HQL and criteria API queries with LINQ expressions. In other words, I'll generate the query in code (as a LINQ expression) and then pass it to NHibernate.Linq and NHib to convert it into a database query.
FYI there is an alpha version available.
I have planed to start using Linq2Nibernate but haven't got round to i yet.
My reason for wanting to user Linq2Nibernate is the nice syntax when constructing criterions and later querying them out.
Here is a nice simple example.
http://ayende.com/Blog/archive/2007/03/16/Linq-for-NHibernate.aspx
I am using Linq2Nhibernate with my repository pattern that returns IQueryable objects.
As you know, IQueryable is only a query definition - doesn't touch database yet.
Then local requirements are added to the query and finally the object or list is materialized.
Seems to work excellent and prevents unnecessary db queries for partial data at higher abstract layers.
What's Linq2NHibernate? As there are several projects which tried to implement a linq provider for nhibernate but all stopped before reaching completion.
Any linq provider needs to return IQueryable, or better an IEnumerable as that's how linq works. It's convenient to return an IQueryable as you then can re-use existing code to pad additional operators to an already created query (as ctx.Employee which might return IQueryable is already a query)