I want to have a dynamic where condition.
In the following example:
var opportunites = from opp in oppDC.Opportunities
join org in oppDC.Organizations
on opp.OrganizationID equals org.OrgnizationID
where opp.Title.StartsWith(title)
select new
{
opp.OpportunityID,
opp.Title,
opp.PostedBy,
opp.Address1,
opp.CreatedDate,
org.OrganizationName
};
Some times I have Title and sometimes I don't. And also I want to add date in where clause dynamically.
For example, like this SQL:
string whereClause;
string SQL = whereClause == string.Empty ?
"Select * from someTable" : "Select * from someTable" + whereclause
You can rewrite it like this:
var opportunites = from opp in oppDC.Opportunities
join org in oppDC.Organizations on opp.OrganizationID equals org.OrgnizationID
select new
{
opp.OpportunityID,
opp.Title,
opp.PostedBy,
opp.Address1,
opp.CreatedDate,
org.OrganizationName
};
if(condition)
{
opportunites = opportunites.Where(opp => opp.Title.StartsWith(title));
}
EDIT: To answer your question in the comments, yes, you can keep appending to the original Queryable. Remember, this is all lazily executed, so at this point all it's doing it building up the IQueryable so you can keep chaining them together as needed:
if(!String.IsNullOrEmpty(title))
{
opportunites = opportunites.Where(.....);
}
if(!String.IsNullOrEmpty(name))
{
opportunites = opportunites.Where(.....);
}
You can dynamically add a where clause to your IQueryable expression like this:
var finalQuery = opportunities.Where( x => x.Title == title );
and for the date similarly.
However, you will have to wait to create your anonymous type until after you've finished dynamically added your where clauses if your anonymous type doesn't contain the fields you want to query for in your where clause.
So you might have something that looks like this:
var opportunities = from opp in oppDC.Opportunities
join org in oppDC.Organizations on
opp.OrganizationID equals org.OrgnizationID
select opp
if(!String.IsNullOrEmpty(title))
{
opportunities = opportunities.Where(opp => opp.Title == title);
}
//do the same thing for the date
opportunities = from opp in opportunities
select new
{
opp.OpportunityID,
opp.Title,
opp.PostedBy,
opp.Address1,
opp.CreatedDate,
org.OrganizationName
};
The WHERE clause could be done something like
//...
where string.IsNullOrEmpty(title) ? true : opp.Title.StartsWith(title)
//...
Dynamically returning records I don't think is possible in LINQ since it needs to be able to create a consistent AnonymousType (in the background)
Because queries are composable, you can just build the query in steps.
var query = table.Selec(row => row.Foo);
if (someCondition)
{
query = query.Where(item => anotherCondition(item));
}
If you know in advance all possible where queries like in the SQL example you have given you can write the query like this
from item in Items
where param == null ? true : ni.Prop == param
select item;
if you don't know all possible where clauses in advance you can add where dymically for example like this:
query = query.Where(item => item.ID != param);
The following questions and answers address this quite well:
Dynamic where clause in LINQ - with column names available at runtime
Is there a pattern using Linq to dynamically create a filter?
I was searching for creating a dynamic where clause in LINQ and came across a very beautifull solution on the web which uses ExpressionBuilder in C#.
I am posting it here since none of the above solution uses this approach. It helped me. Hope it helps you too
http://www.codeproject.com/Tips/582450/Build-Where-Clause-Dynamically-in-Linq
Related
I have this here Linq query using lambda expressions and its throwing an error
A query body must end with a select clause or a group clause
Here is the query in question
var query = from county in HWC.StateCounties.Where(w => w.StateID == id).Select(s => new CountyList
{
CountyID = s.StateCountyID,
CountyName = s.CountyName
});
I even tried adding a .Tolist() at the end and got the same error.
Why is this happening when I clearly have a select clause?
I made a mistake in my query, the query should be this instead
var query = HWC.StateCounties.Where(w => w.StateID == id).Select(s => new
{
s.StateCountyID,
s.CountyName
});
Although it is possible to combine Linq and extensions methods, a Linq query always needs to end with select in c# (In vb this is not necessary).
Maybe it is a matter of taste, but I prefer Linq over extension methods because it makes the code far more readable because all braces are removed.
Your query will look like
var query =
from county in HWC.StateCounties
where county.stateID == id
select new
{
county.StateCountyID,
county.CountyName,
};
If you want to combine the query will look like:
var query =
from county in HWC.StateCounties.Where(s => s.stateID == id)
select new
{
county.StateCountyID,
county.CountyName,
};
Here is my try of dynamic Linq query with join. I try to get list of unique categories, brands and other criteria which were present in last reading in database. What is passed to the query (brand, category etc.) would only be defined at runtime.
I read about best way of doing this with func's, predicates etc., I think this is beyond my capacity at this stage. I'm trying the easier way with query string, which I got working for some simpler case, but I'm doing something wrong here with join. If I do just plain select product.Category with intellisense of course this works, but not in string in select clause.
public IEnumerable<string> getFilterItems(string dbColumn)
{
var filterItems = new List<string>();
return (from reading in Helper.LatestReadings
where reading.Distributor != Helper.Client
join product in Helper.Context.Products
on reading.ProductId equals product.SkuCode
select ("product." + dbColumn)).Distinct();
}
you can use reflection to achieve this
public IEnumerable<string> getFilterItems(string dbColumn)
{
var filterItems = new List<string>();
var productList = from reading in Helper.LatestReadings
where reading.Distributor != Helper.Client
join product in Helper.Context.Products
on reading.ProductId equals product.SkuCode
select product;
return productList.Select(x=>x.GetType().GetProperty(dbColumn).GetValue(x)).Cast<string>().Distinct();
}
"product." + dbColumn evaluates to a String, therefore select ("product." + dbColumn) will return this string n times, one time per item in the result of your query.
This SO question has an answer if you want to have a dynamic select. It proposes a method so that you could write something like
var result = list.Select( CreateNewStatement( "Field1, Field2" ) );
EDIT:
Oh, sorry, I just read about "dynamic LINQ" here, therefore my above answer may not be that helpful. As I can see on the linked page, they use the following format in Select.
.Select("new(<ColumnName> as <DataMemberName>, ... )");
In your case you should try
.Select("new(product" + dbColumn + " as Value)");
I'm new to linq. I need to run a query that joins two columns (AnonymousUser.AnonymousId being uniqueidentifier and comment.UserId being nvarchar(100)), something like below:
using (CommentEntities db = new CommentEntities())
{
// filteredComments is a query that is not run until the next .ToList()
IQueryable<Comment> filteredComments = this.CommentGetList(...);
var query = from comment in filteredComments
// following line is the syntax error, because columns' types don't match
join user in db.AnonymousUsers on comment.UserId equals user.AnonymousId into gj
from userNull in gj.DefaultIfEmpty()
select new CommentWithName
{
Comment = comment,
UserId = comment.UserId,
FirstName = (userNull == null ? "" : userNull.Name),
LastName = "",
Email = (userNull == null ? "" : userNull.Email)
};
return query.ToList();
}
First I was happy writing the query with .ToString() ! As it turns out that entity framework doesn't know how to translate it to sql. The same is true for Guid.Parse(string). Also new Guid(string) cannot be used in linq to entities (only parameterless constructors allowed)!
So after searching, I found out it's not possible doing such thing in EF 4.0! I migrated my code to a stored procedure that I'm not really happy about it.
Is it possible to tell entity framework to use a CAST in SQL?
Is there any solutions to this problem? Is there any way that I can bring the logic in code?
NOTE: I meant to do it in one GO. Otherwise one possible solution is to get Entities from first table, and put the Ids in a list and get entities from second table.
call toList() before applying those methods. Like:
var Product = db.Products.Where(p => p.ProductId == Guid.Parse("B4E913F9-166C-49BA-AADE-6DB889D1756F")).Single();
Would throw a
c# LINQ to Entities does not recognize the method "System.Guid Parse" (System.String)' method, and this method cannot be translated into a store expression
But this works:
var Product = db.Products.ToList().Where(p => p.ProductId == Guid.Parse("B4E913F9-166C-49BA-AADE-6DB889D1756F")).Single()
p.s.: I think you will lose lazyloading but you can do eagerloading with .Include before calling .ToList().
If your list is object list you could convert it to the type which has Guid as identifier, first create new anonymous type and then filter it base on UserId, sure UserId which is of type int, wont include in join:
int output = 0;
var secondList = list.Where(x=>!int.TryParse(x.UserID, out output))
.Select(x=>new {Comment = x, ID = new Guid(x.UserID))
.ToList();
Now you could run your query on db by using secondList.
I am trying to do a dynamic order by on columns using Marc Gravell's code. I am posting the 2 queries. It works in one case but doesn't work in 2nd case. Can anybody tell me what changes I need to make to make both queries run perfectly?
This is the link to the Marc Gravell's answer:
https://stackoverflow.com/a/233505
I am using Northwind database. These are both my queries:
var query = (from cust in northwindEntities.Customers
select new
{
City = cust.City ,
Orders = northwindEntities.Orders
.Where(o => o.CustomerID == cust.CustomerID)
.OrderBy("OrderID")
}); // doesn't work.
var query = (from cust in northwindEntities.Customers
select new
{
City = cust.City ,
//Orders = northwindEntities.Orders.Where(o => o.CustomerID == cust.CustomerID).
// OrderBy("OrderID")
}).OrderBy("City"); // works
Here is the exception of the 1st query:
LINQ to Entities does not recognize the method
'System.Linq.IOrderedQueryable1[ConsoleApplication12.Order]
OrderBy[Order](System.Linq.IQueryable1[ConsoleApplication12.Order],
System.String)' method, and this method cannot be translated into a
store expression.
You need to order the final set of result, like you do it in the second case. In first case you order only northwindEntities.Orders.Where( result and not final one.
The correct query is the second.
Obviously it would not work because of the same reason as
var query = (from cust in northwindEntities.Customers
select new
{
City = cust.City ,
Orders = northwindEntities.Orders
.MyCustomMethod()
});
will not work. LINQ-to-Entities will walk through this expression tree and try to convert it to SQL. It can work on known sub set of methods to translate to SQL.
But in the second query, custom OrderBy method dynamically creates the OrderBy that LINQ-to-Entities knows.
Im working on an source code with an sql query in a VAR type like
var query = select ... from ... where ... ;
is it possible to add an dynamic "where clause" like
string condition = "where x.x > x.y";
e.g. var query = select ... from ... + condition;
Iam sorry for my bad english
You are not clearly stating how your query looks like. Is it a result of a LINQ operation or simply a String?
The keyword var is only usable for design time. The compiler will substitute it with the correct datatype.
If you SQL query is a string, like
var query = "Select ... from ... where ..";
then
string condition = "where x.x > x.y";
query += condition;
is valid because both variables are strings. You can't combine a non string type with a string the way your code suggests.
I do now assume that you are using a LINQ syntax. It is possible to add such conditions to a linq query per code, I think the keywords linq query builder, expression tree and predicate should get you started.
I'd strongly suggest that you stop using the var keyword without exactly knowing what it does and where to use it.
Dynamic Linq exists specifically to solve late-bound scenarios for LINQ:
http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx
Allows constructs such as:
NorthwindDataContext northwind = new NorthwindDataContext();
var query = northwind.Products
.Where("CategoryID = 3 AND UnitPrice > 3")
.OrderBy("SupplierID");
If you do not call ToList() and your final mapping to the DTO type, you can add Where clauses as you go, and build the results at the end:
var query = from u in DataContext.Users
where u.Division == strUserDiv
&& u.Age > 18
&& u.Height > strHeightinFeet
select u;
if (useAge)
query = query.Where(u => u.Age > age);
if (useHeight)
query = query.Where(u => u.Height > strHeightinFeet);
// Build the results at the end
var results = query.Select(u => new DTO_UserMaster
{
Prop1 = u.Name,
}).ToList();
This will still only result in a single call to the database, which will be effectively just as efficient as writing the query in one pass.
I saw this answer here by Reed Copsey