Is this a correct way of retreiving data from database using linq?
var c= using db in db.c where c.id==id
Is this a correct way of retreiving data from database using linq?
partially yes.
It's better to write your query inside a method like this:
public static Product GetProduct(int id, string name)
{
DBNameDataContext myDB = new DBNameDataContext();
var product = from p in myDB.Products
where p.ID == id
&& p.Name == name
select p;
return product;
}
and then in your main code you can get your Product as below:
var product = GetProduct(5, "C# in Depth");
(Sample code is in C#)
Related
I am working on Database First Approach in Entity Framework where I have to retrieve specific columns from the Entity.
Public IQueryable<Entity.Employees> GetEmployeeName(String FName,String LName)
{
var query = (from s in Employees
where s.firstName = FName && s.lastName = LName
select new {s.firstName, s.middleName});
return query;
}
Here return statement is throwing an error where it seems that its not matching with Employees (entity) columns. Could you please help me in sorting out this issue? Thanks in advance.
You need to use == for comparison, also you need to use dynamic type as return type since you are returning a custom anonymous type. Try this
Public IQueryable<dynamic> GetEmployeeName(String FName,String LName)
{
var query=(from s in Employees
where s.firstName==FName && s.lastName==LName
select new {s.firstName,s.middleName});
return query.AsQueryable();
}
Finally you will use it like below, keep in mind that intelisense won't work on dynamic object.
var query = GetEmployeeName("Jake", "Smith");
List<dynamic> results = query.ToList();
foreach (dynamic result in results)
{
string fristName = result.FirstName;
string lastName = result.MiddleName;
}
I am trying to perform a SELECT on the M1lhao table of Sorteio entity (database).
I don't want to go the traditional "string query" or AddWithParameter() way, i wanted to use the MVC4 EF5 available methods.
The following code passes the entire Table to the View, that i can do a foreach in the View and all works fine. What i am looking for is how can i do a SQL query, so i can pass only the element(s) i want, sorted DESCending (for example), obviously on a List and obeying the Model that the View expects.
Essentially i want a replacement for (i tried variants too, db.Milhao, etc):
var data = db.Database.ExecuteSqlCommand("SELECT * From M1lhao WHERE DrawID = {0}", id);
The problem with Find() is that it only searches primary keys.
The complete code:
public class M1lhaoController : Controller
{
private Sorteio db = new Sorteio();
public ActionResult Index(int id = 1)
{
var data = db.Database.ExecuteSqlCommand("SELECT * From M1lhao WHERE DrawID = {0}", id); // the variable data comes as -1
M1lhao m1lhao = db.M1lhao.Find(id);
if (m1lhao == null)
{
return HttpNotFound();
}
return View(db.M1lhao.ToList());
}
}
Thank you.
You can try as shown below.
var data = db.M1lhao.Where(m=>m.DrawID == id).Select(p=>p);
You can learn more about Method-Based Query Syntax : Projection
I have a linq object and I want to write the query using linq.
please help me.
INPUT:
var tags = (from row in tempChildData.AsEnumerable()
join tagOrder in tupleInfoDataset.Tables["TagHierarchy"].AsEnumerable() on row.Field<Int64>("TAGID") equals tagOrder.Field<Int64>("TAGID")
join tagName in tupleInfoDataset.Tables["SequenceChoiceList"].AsEnumerable() on tagOrder.Field<Int64>("PARENTTAGID") equals tagName.Field<Int64>("TAGID")
join facet in tupleInfoDataset.Tables["FacetType"].AsEnumerable() on tagName.Field<string>("Tag_Name") equals facet.Field<string>("Facetname")
join tagIdInfo in schDataTogetTagid.AsEnumerable() on row.Field<string>("refTagName").Contains(":") ? row.Field<string>("refTagName").Split(':').Last():row.Field<string>("refTagName") equals tagIdInfo.Field<string>("TAGNAME")
where ( childList.Contains(row.Field<Int64>("TAGID")) && facet.Field<string>("FacetType").ToLower().Equals("ctype"))
select new
{
Tagid = row.Field<Int64>("TAGID"),
TagIdToInsert=tagIdInfo.Field<Int64>("TAGID"),
MaxOccur = row.Field<string>("Maxoccurs"),
MinOccur =Convert.ToInt32(Convert.ToString(row.Field<string>("Minoccur"))),
ParentTagId=tagOrder.Field<Int64>("PARENTTAGID"),
Order=tagOrder.Field<Int64>("TAG_ORDER"),
ParentTagname = tagName.Field<string>("Tag_Name"),
FacetId=facet.Field<Int64>("FacetID")
}).ToList();
var parentTagID = (from tagIdInfo in tupleInfoDataset.Tables["Tuple"].AsEnumerable()
where tagIdInfo.Field<Int64>("TAGID").Equals(key.Key)
select tagIdInfo.Field<Int64>("ConceptID")).ToList();
long parentID =Convert.ToInt64(parentTagID[0]);
Now i want the query out of the above code as:
INSERT INTO TUPLE_MAP (TagId,ParentTagId,ParentTagname,MinOccur,MaxOccur,Order)
VALUES (TagIdToInsert,ParentTagId,ParentTagname,MinOccur,MaxOccur,Order)
Please help me I don't know how to write SQL queries using linq
Maybe something like this:
using(var db=new DataContext("YourConnectionStringHERE"))
{
db.TUPLE_MAP.InsertAllOnSubmit(tags.Select (t =>
new TUPLE_MAP()
{
TagId=t.TagIdToInsert,
ParentTagId=t.ParentTagId,
ParentTagname=t.ParentTagname,
MinOccur=t.MinOccur,
MaxOccur=t.MaxOccur,
Order=t.Order
}));
db.SubmitChanges();
}
Or if you want to use the parentID then something like this:
using(var db=new DataContext("YourConnectionStringHERE"))
{
db.TUPLE_MAP.InsertAllOnSubmit(tags.Select (t =>
new TUPLE_MAP()
{
TagId=t.TagIdToInsert,
ParentTagId=parentID,
ParentTagname=t.ParentTagname,
MinOccur=t.MinOccur,
MaxOccur=t.MaxOccur,
Order=t.Order
}));
db.SubmitChanges();
}
where db is your linq data context
Useful references:
How to: Insert Rows Into the Database (LINQ to SQL)
EDIT
So if you are using the Compact database 3.5 then many something like this:
using (var conn =new SqlCeConnection("Data Source = test.sdf; Password ='pass'"))
{
foreach (var tag in tags)
{
using(var cmd = conn.CreateCommand())
{
cmd.CommandText = #"INSERT INTO TUPLE_MAP (TagId,ParentTagId,ParentTagname,MinOccur,MaxOccur,Order)
VALUES (#TagIdToInsert,#ParentTagId,#ParentTagname,#MinOccur,#MaxOccur,#Order)";
cmd.Parameters.AddWithValue("#TagIdToInsert", tag.TagIdToInsert);
cmd.Parameters.AddWithValue("#ParentTagId", tag.ParentTagId);
cmd.Parameters.AddWithValue("#ParentTagname", tag.ParentTagname);
cmd.Parameters.AddWithValue("#MinOccur", tag.MinOccur);
cmd.Parameters.AddWithValue("#MaxOccur", tag.MaxOccur);
cmd.Parameters.AddWithValue("#Order", tag.Order);
cmd.ExecuteNonQuery();
}
}
}
Useful references:
Why can't I insert a record into my SQL Compact 3.5 database?
SqlCeCommand.Parameters Property
SqlCeCommand Class
SqlParameterCollection.AddWithValue Method
Use linq Pad or sql profiler to see the generated SQL.
You can also use visual studio for that purpose. In the debug mode,hold cursor on the variable "tags", you will be able to see the SQL.
I am assuming you are using Linq to SQL, if you are doing so you would have entity called Tuple_map in you xxxDataContext. Then you would just have to create object of that entity something like this....
using (XXXDataContext context = new XXXDataContext())
{
Tuple_map obj = new Tuple_map();
//Populate obj properties like obj.tabid = from objects you got it from above query
context.Tuple_map.InsertOnSubmit(obj);
context.SubmitChanges();
}
I have a webservice I call from a WP7 app. I get a list of high scores in a table (name/score).. What is the simpliest way to add a 3rd column on the far left which is simply the row?
Do I need to add a property to the entity? Is there someway to get the row #?
I tried these things below with no success..
[OperationContract]
public List<DMHighScore> GetScores()
{
using (var db = new DMModelContainer())
{
// return db.DMHighScores.ToList();
var collOrderedHighScoreItem = (from o in db.DMHighScores
orderby o.UserScore ascending
select new
{
o.UserName,
o.UserScore
}).Take(20);
var collOrderedHighScoreItem2 = collOrderedHighScoreItem.AsEnumerable().Select((x, i) => new DMHighScoreDTO
{
UserName = x.UserName,
UserScore = x.UserScore
}).ToList();
}
}
[DataContract]
public class DMHighScoreDTO
{
int Rank;
string UserName;
string UserScore;
}
So lets assume you want to load top 100 users in leaderboard and you want to have their rank included:
[OperationContract]
public List<ScoreDto> GetTop100()
{
// Linq to entities query
var query = (from u from context.Users
order by u.Score
select new
{
u.Name,
u.Score
}).Take(100);
// Linq to objects query from working on 100 records loaded from DB
// Select with index doesn't work in linq to entities
var data = query.AsEnumerable().Select((x, i) => new ScoreDto
{
Rank = i + 1,
Name = x.Name,
Score = x.Score
}).ToList();
return data;
}
what will the row number be used for? if this is for ordering might I suggest adding a column named Order, then map the column to your entity.
if you require a row index, you could also call the .ToList() on the query and fetch the index locations for each entity.
Edit:
you could add the Rank property and set it to Ignore. This will enable you to go through the collection set the rank with a simple for loop. This will also not be persisted in the database. It will also not have any required columns in the database.
It does add an extra iteration.
the other way to go about it. This would be to add the rank number in the generated UI and not in the data collection being used to bind.
Is this even possible? It seems like I should be able to.
This is my issue. I need to run a web service method from a 3rd party to get a collection of available items where I need the ID and a Status property. Then I have method using LINQ to SQL that retrieves the items that are current.
What I need to do is retrieve the items that are current and available. I can connect them through ID BUT I also need the Status returned from the web service method.
Ideally, my final results will be the same results as from the LINQ to SQL method plus the Status property from the web service method.
Any assistance would be appreciated. Thanks!
Below is what I want to do. Have a method that takes in the list of objects from the web service and join with the existing query.
public List<Items> GetItems(List<AvailableItems> availList)
{
var result = (from c in dataContext.items
where c.status == "current"
select c;
return result;
}
public List<Item> GetItems(List<AvailableItems> availList)
{
var result = (from c in dataContext.items.AsEnumerable())
join a in availList on a.id equals c.id
where c.status == "current"
select c;
return result.ToList();
}
Re-Edit:
I typically extract the ids as a lookup list, and do the following:
public List<Items> GetItems(List<AvailableItems> availList)
{
var availableItemIds = availList.Select(a => a.Id).ToList();
var items = (from item in dataContext.items
where availableItemIds.Contains(item.Id)
where item.status == "current"
return items;
}