linq: Using methods in select clause - linq

I'm breaking my head with this and decided to share my problem with you
I want to create an anonymous select from several tables, some of them may contain more than one result. i want to concatenate these results into one string
i did something like this:
var resultTable = from item in dc.table
select new
{
id= item.id,
name= CreateString((from name in item.Ref_Items_Names
select name.Name).ToList()),
};
and the CreateString() is:
private string CreateString(List<string> list)
{
StringBuilder stringedData = new StringBuilder();
for (int i = 0; i < list.Count; i++)
{
stringedData.Append(list[i] + ", ");
}
return stringedData.ToString();
}
my intentions were to convert the "name" query to list and then sent it to CreateString() to convert it to one long concatenated string.
I tried using .Aggregate((current,next) => current + "," + next);
but when i try to convert my query to DataTable like below:
public DataTable ToDataTable(Object query)
{
DataTable dt = new DataTable();
IDbCommand cmd = dc.GetCommand(query as IQueryable);
SqlDataAdapter adapter = new SqlDataAdapter();
adapter.SelectCommand = (SqlCommand)cmd;
cmd.Connection.Open();
adapter.Fill(dt);
cmd.Connection.Close();
return dt;
}
I'm getting exception that "dc.GetCommand()" can't understand query with Aggregate method
later I tried to even use this simple query:
var resultTable = from itemin dc.table
select new
{
name = CreateString()
};
When CreateString() returns "success", nothing was inserted to "name"
why there is no way of using methods in select clause?
Thank you
Yotam

There is difference between LINQ to objects and LINQ to some-db-provider. Generally speaking, when using IQueryable, you can't use any methods, except the ones your provider understands.
What you can do is to retrieve the data from the database and then do the formatting using LINQ to objects:
var data = from item in dc.table
where /* some condition */
select item;
var result = from item in data.AsEnumerable()
select new
{
name = SomeFunction(item)
}
The AsEnumerable() extension method forces processing using LINQ to objects.

Forgive me if I've miss interpreted your question. It seems that what you are trying to do is abstract your select method for reuse. If this is the case, you may consider projection using a lambda expression. For example:
internal static class MyProjectors
{
internal static Expression<Func<Object1, ReturnObject>> StringDataProjector
{
get
{
return d => new Object1()
{
//assignment here
}
}
}
}
Now you can select your datasets as such:
dc.Table.Select(MyProjectors.StringDataProjector)
As for the concatenation logic, what about selecting to some base class with an IEnumerable<string> property and a read-only property to handle the concatenation of the string?

Related

LINQ to Entities does not recognize the method , method cannot be translated into a store expression

private void BindGrid()
{
AdvContextEF db = new AdvContextEF();
var query = from r in db.mytable
orderby r.CreateDate descending
select new
{
r.id,
r.code,
r.mytable.relatedtables[0].TheCenter.Name
};
RadGrid1.DataSource = query.ToList();
RadGrid1.DataBind();
}
I got the following error when running the code above.
LINQ to Entities does not recognize the method 'AdvContextEF.mymethod get_Item(Int32)' method, and this method cannot be translated into a store expression.
thank you
Instead of trying to index into r.mytable.relatedtables[0], try using .FirstOrDefault().
r.mytable.relatedtables.FirstOrDefault().TheCenter.Name
or
Name = r.mytable.relatedtables.Select(rt => rt.TheCenter.Name).FirstOrDefault()

Explicit construction of entity type in query is not allowed [duplicate]

Using Linq commands and Linq To SQL datacontext, Im trying to instance an Entity called "Produccion" from my datacontext in this way:
Demo.View.Data.PRODUCCION pocoProduccion =
(
from m in db.MEDICOXPROMOTORs
join a in db.ATENCIONs on m.cmp equals a.cmp
join e in db.EXAMENXATENCIONs on a.numeroatencion equals e.numeroatencion
join c in db.CITAs on e.numerocita equals c.numerocita
where e.codigo == codigoExamenxAtencion
select new Demo.View.Data.PRODUCCION
{
cmp = a.cmp,
bonificacion = comi,
valorventa = precioEstudio,
codigoestudio = lblCodigoEstudio.Content.ToString(),
codigopaciente = Convert.ToInt32(lblCodigoPaciente.Content.ToString()),
codigoproduccion = Convert.ToInt32(lblNroInforme.Content.ToString()),
codigopromotor = m.codigopromotor,
fecha = Convert.ToDateTime(DateTime.Today.ToShortDateString()),
numeroinforme = Convert.ToInt32(lblNroInforme.Content.ToString()),
revisado = false,
codigozona = (c.codigozona.Value == null ? Convert.ToInt32(c.codigozona) : 0),
codigoclinica = Convert.ToInt32(c.codigoclinica),
codigoclase = e.codigoclase,
}
).FirstOrDefault();
While executing the above code, I'm getting the following error that the stack trace is included:
System.NotSupportedException was caught
Message="The explicit construction of the entity type 'Demo.View.Data.PRODUCCION' in a query is not allowed."
Source="System.Data.Linq"
StackTrace:
en System.Data.Linq.SqlClient.QueryConverter.VisitMemberInit(MemberInitExpression init)
en System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node)
en System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node)
en System.Data.Linq.SqlClient.QueryConverter.VisitSelect(Expression sequence, LambdaExpression selector)
en System.Data.Linq.SqlClient.QueryConverter.VisitSequenceOperatorCall(MethodCallExpression mc)
en System.Data.Linq.SqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc)
en System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node)
en System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node)
en System.Data.Linq.SqlClient.QueryConverter.VisitFirst(Expression sequence, LambdaExpression lambda, Boolean isFirst)
en System.Data.Linq.SqlClient.QueryConverter.VisitSequenceOperatorCall(MethodCallExpression mc)
en System.Data.Linq.SqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc)
en System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node)
en System.Data.Linq.SqlClient.QueryConverter.ConvertOuter(Expression node)
en System.Data.Linq.SqlClient.SqlProvider.BuildQuery(Expression query, SqlNodeAnnotations annotations)
en System.Data.Linq.SqlClient.SqlProvider.System.Data.Linq.Provider.IProvider.Execute(Expression query)
en System.Data.Linq.DataQuery`1.System.Linq.IQueryProvider.Execute[S](Expression expression)
en System.Linq.Queryable.FirstOrDefault[TSource](IQueryable`1 source)
en Demo.View.InformeMedico.realizarProduccionInforme(Int32 codigoExamenxAtencion, Double precioEstudio, Int32 comi) en D:\cs_InformeMedico\app\InformeMedico.xaml.cs:línea 602
en Demo.View.InformeMedico.UpdateEstadoEstudio(Int32 codigo, Char state) en D:\cs_InformeMedico\app\InformeMedico.xaml.cs:línea 591
en Demo.View.InformeMedico.btnGuardar_Click(Object sender, RoutedEventArgs e) en D:\cs_InformeMedico\app\InformeMedico.xaml.cs:línea 683
InnerException:
Is that now allowed in LINQ2SQL?
Entities can be created outside of queries and inserted into the data store using a DataContext. You can then retrieve them using queries. However, you can't create entities as part of a query.
I am finding this limitation to be very annoying, and going against the common trend of not using SELECT * in queries.
Still with c# anonymous types there is a workaround, by fetching the objects into an anonymous type, and then copy it over into the correct type.
For example:
var q = from emp in employees where emp.ID !=0
select new {Name = emp.First + " " + emp.Last, EmployeeId = emp.ID }
var r = q.ToList();
List<User> users = new List<User>(r.Select(new User
{
Name = r.Name,
EmployeeId = r.EmployeeId
}));
And in the case when we deal with a single value (as in the situation described in the question) it is even easier, and we just need to copy directly the values:
var q = from emp in employees where emp.ID !=0
select new { Name = emp.First + " " + emp.Last, EmployeeId = emp.ID }
var r = q.FirstOrDefault();
User user = new User { Name = r.Name, EmployeeId = r.ID };
If the name of the properties match the database columns we can do it even simpler in the query, by doing select
var q = from emp in employees where emp.ID !=0
select new { emp.First, emp.Last, emp.ID }
One might go ahead and write a lambda expression that can copy automatically based on the property name, without needing to specify the values explictly.
Here's another workaround:
Make a class that derives from your LINQ to SQL class. I'm assuming that the L2S class that you want to return is Order:
internal class OrderView : Order { }
Now write the query this way:
var query = from o in db.Order
select new OrderView // instead of Order
{
OrderID = o.OrderID,
OrderDate = o.OrderDate,
// etc.
};
Cast the result back into Order, like this:
return query.Cast<Order>().ToList(); // or .FirstOrDefault()
(or use something more sensible, like BLToolkit / LINQ to DB)
Note: I haven't tested to see if tracking works or not; it works to retrieve data, which is what I needed.
I have found that if you do a .ToList() on the query before trying to contruct new objects it works
I just ran into the same issue.
I found a very easy solution.
var a = att as Attachment;
Func<Culture, AttachmentCulture> make =
c => new AttachmentCulture { Culture = c };
var culs = from c in dc.Cultures
let ac = c.AttachmentCultures.SingleOrDefault(
x => x.Attachment == a)
select ac == null ? make(c) : ac;
return culs;
I construct an anonymous type, use IEnumerable (which preserves deferred execution), and then re-consruct the datacontext object. Both Employee and Manager are datacontext objects:
var q = dc.Employees.Where(p => p.IsManager == 1)
.Select(p => new { Id = p.Id, Name = p.Name })
.AsEnumerable()
.Select(item => new Manager() { Id = item.Id, Name = item.Name });
Within the book "70-515 Web Applications Development with Microsoft .NET Framework 4 - Self paced training kit", page 638 has the following example to output results to a strongly typed object:
IEnumerable<User> users = from emp in employees where emp.ID !=0
select new User
{
Name = emp.First + " " + emp.Last,
EmployeeId = emp.ID
}
Mark Pecks advice appears to contradict this book - however, for me this example still displays the above error as well, leaving me somewhat confused. Is this linked to version differences? Any suggestions welcome.
I found another workaround for the problem that even lets you retain your result as IQueryale, so it doesn't actually execute the query until you want it to be executed (like it would with the ToList() method).
So linq doesn't allow you to create an entity as a part of query? You can shift that task to the database itself and create a function that will grab the data you want. After you import the function to your data context, you just need to set the result type to the one you want.
I found out about this when I had to write a piece of code that would produce a IQueryable<T> in which the items don't actually exist in the table containing T.
pbz posted a work around by creating a View class inherited from an entity class that you could be working with. I'm working with a dbml model of a table that has > 200 columns. When I try and return the whole table I get "Root Element missing" errors. I couldn't find anyone who wanted to deal with my particular issue so I was looking at rewriting my entire approach. Just creating a view class for the entitiy class worked in my case.
As pbz suggests : Create a view class that inherits from your entity class. For me this is tbCamp so :
internal class tbCampView : tbCamp
{
}
Then use the view class in your query :
using (var dc = ConnectionClass.Connect(Dev))
{
var camps = dc.tbCamps.Select(s => new tbCampView
{
active = s.active,
idCamp = s.idCamp,
campName = s.campName
});
SmartTableViewer(camps, dg1);
}
private void SmartTableViewer<T>(IEnumerable<T> allRecords)
{
// Build sorted rows back into new table
var table = new DataTable();
// Create columns based on type
if (allRecords is IEnumerable<tbCamp> tbCampRecords)
{
// Get the columns you want
table.Columns.Add("idCamp");
table.Columns.Add("campName");
foreach (var record in tbCampRecords)
{
// Make a new row
var r = table.NewRow();
// Add the contents to each column of the row
r["idCamp"] = record.idCamp;
r["campName"] = record.campName;
// Add the row to the table.
table.Rows.Add(r);
}
}
else
{
MessageBox.Show("Unhandled type. Add support for new data type in SmartTableViewer()");
return;
}
// Update table in grid
dg1.DataSource = table.DefaultView;
}
Here is what happens when you try and create an entity class object in the query.
I didn't want to have to use an anonymous type if I could help it because I wanted the type to be tbCamp. Since tbCampView is of type tbCamp the is operator works well. see Brian Hasden's answer Passing a generic List<> in C#
I'm surprised this is even an issue but with larger tables I run into this error so I thought I would just show it here :
When trying to read this table into memory I get the following error. There are < 2000 rows but the columns are > 200 for each. I don't know if that is an issue or not.
If I just want a few columns I need to create a custom class and handle that which isn't that big of a pain. With the approach pbz provided I don't have to worry about it.
Here is the entire project in case it helps someone.
public partial class Form1 : Form
{
private const bool Dev = true;
public Form1()
{
InitializeComponent();
}
private void btnGetAllCamps_Click(object sender, EventArgs e)
{
using (var dc = ConnectionClass.Connect(Dev))
{
IQueryable<tbCampView> camps = dc.tbCamps.Select(s => new tbCampView
{
// Project columns as needed.
active = s.active,
idCamp = s.idCamp,
campName = s.campName
});
// pass in as a
SmartTableViewer(camps);
}
}
private void SmartTableViewer<T>(IEnumerable<T> allRecords)
{
// Build sorted rows back into new table
var table = new DataTable();
// Create columns based on type
if (allRecords is IEnumerable<tbCamp> tbCampRecords)
{
// Get the columns you want
table.Columns.Add("idCamp");
table.Columns.Add("campName");
foreach (var record in tbCampRecords)
{
//var newRecord = record;
// Make a new row
var r = table.NewRow();
// Add the contents to each column of the row
r["idCamp"] = record.idCamp;
r["campName"] = record.campName;
// Add the row to the table.
table.Rows.Add(r);
}
}
else
{
MessageBox.Show("Unhandled type. Add support for new data type in SmartTableViewer()");
return;
}
// Update table in grid
dg1.DataSource = table.DefaultView;
}
internal class tbCampView : tbCamp
{
}
}

How to access data into IQueryable?

I have IQueryable object and I need to take the data inside the IQueryable to put it into Textboxs controls. Is this possible?
I try something like:
public void setdata (IQueryable mydata)
{
textbox1.text = mydata.????
}
Update:
I'm doing this:
public IQueryable getData(String tableName, Hashtable myparams)
{
decimal id = 0;
if (myparams.ContainsKey("id") == true)
id = (decimal)myparams["id"];
Type myType= Type.GetType("ORM_Linq." + tableName + ", ORM_Linq");
return this.GetTable(tableName , "select * from Articu where id_tipo_p = '" + id + "'");
}
public IQueryable<T> GetTable<T>(System.Linq.Expressions.Expression<Func<T, bool>> predicate) where T : class
{
return _datacontext.GetTable<T>().Where(predicate);
}
This returns a {System.Data.Linq.SqlClient.SqlProvider+OneTimeEnumerable1[ORM_Linq.Articu]}`
I don't see any method like you tell me. I see Cast<>, Expression, ToString...
EDIT: Updated based on additional info from your other posts...
Your getData method is returning IQueryable instead of a strongly typed result, which is why you end up casting it. Try changing it to:
public IQueryable<ORM_Linq.Articu> getData(...)
Are you trying to query for "Articu" from different tables?
With the above change in place, your code can be rewritten as follows:
ORM_Linq.Articu result = mydata.SingleOrDefault();
if (result != null)
{
TextBoxCode.Text = result.id.ToString();
TextBoxName.Text = result.descrip;
}
If you have a single result use SingleOrDefault which will return a default value if no results are returned:
var result = mydata.SingleOrDefault();
if (result != null)
{
textbox1.text = result.ProductName; // use the column name
}
else
{
// do something
}
If you have multiple results then loop over them:
foreach (var item in mydata)
{
string name = item.ProductName;
int id = item.ProductId;
// etc..
}
First, you should be using a strongly-typed version of IQueryable. Say that your objects are of type MyObject and that MyObject has a property called Name of type string. Then, first change the parameter mydata to be of type IQueryable<MyObject>:
public void setdata (IQueryable<MyObject> mydata)
Then we can write a body like so to actually get some data out of. Let's say that we just want the first result from the query:
public void setdata (IQueryable<MyObject> mydata) {
MyObject first = mydata.FirstOrDefault();
if(first != null) {
textbox1.Text = first.Name;
}
}
Or, if you want to concatenate all the names:
public void setdata(IQueryable<MyObject> mydata) {
string text = String.Join(", ", mydata.Select(x => x.Name).ToArray());
textbo1.Text = text;
}
Well, as the name suggests, an object implementing IQueryable is... Queryable! You'll need to write a linq query to get at the internal details of your IQueryable object. In your linq query you'll be able to pull out its data and assign bits of it where ever you'd like - like your text box.
Here's a great starting place for learning Linq.
I think you find the same mental struggle when coming from FoxPro and from DataSet. Really nice, powerful string-based capabilities(sql for query, access to tables and columns name) in these worlds are not available, but replaced with a compiled, strongly-typed set of capabilities.
This is very nice if you are statically defining the UI for search and results display against a data source known at compile time. Not so nice if you are trying to build a system which attaches to existing data sources known only at runtime and defined by configuration data.
If you expect only one value just call FirstOrDefault() method.
public void setdata (IQueryable mydata)
{
textbox1.text = mydata.FirstOrDefault().PropertyName;
}

How to dynamically add OR operator to WHERE clause in LINQ

I have a variable size array of strings, and I am trying to programatically loop through the array and match all the rows in a table where the column "Tags" contains at least one of the strings in the array. Here is some pseudo code:
IQueryable<Songs> allSongMatches = musicDb.Songs; // all rows in the table
I can easily query this table filtering on a fixed set of strings, like this:
allSongMatches=allSongMatches.Where(SongsVar => SongsVar.Tags.Contains("foo1") || SongsVar.Tags.Contains("foo2") || SongsVar.Tags.Contains("foo3"));
However, this does not work (I get the following error: "A lambda expression with a statement body cannot be converted to an expression tree")
allSongMatches = allSongMatches.Where(SongsVar =>
{
bool retVal = false;
foreach(string str in strArray)
{
retVal = retVal || SongsVar.Tags.Contains(str);
}
return retVal;
});
Can anybody show me the correct strategy to accomplish this? I am still new to the world of LINQ :-)
You can use the PredicateBuilder class:
var searchPredicate = PredicateBuilder.False<Songs>();
foreach(string str in strArray)
{
var closureVariable = str; // See the link below for the reason
searchPredicate =
searchPredicate.Or(SongsVar => SongsVar.Tags.Contains(closureVariable));
}
var allSongMatches = db.Songs.Where(searchPredicate);
LinqToSql strange behaviour
I recently created an extension method for creating string searches that also allows for OR searches. Blogged about here
I also created it as a nuget package that you can install:
http://www.nuget.org/packages/NinjaNye.SearchExtensions/
Once installed you will be able to do the following
var result = db.Songs.Search(s => s.Tags, strArray);
If you want to create your own version to allow the above, you will need to do the following:
public static class QueryableExtensions
{
public static IQueryable<T> Search<T>(this IQueryable<T> source, Expression<Func<T, string>> stringProperty, params string[] searchTerms)
{
if (!searchTerms.Any())
{
return source;
}
Expression orExpression = null;
foreach (var searchTerm in searchTerms)
{
//Create expression to represent x.[property].Contains(searchTerm)
var searchTermExpression = Expression.Constant(searchTerm);
var containsExpression = BuildContainsExpression(stringProperty, searchTermExpression);
orExpression = BuildOrExpression(orExpression, containsExpression);
}
var completeExpression = Expression.Lambda<Func<T, bool>>(orExpression, stringProperty.Parameters);
return source.Where(completeExpression);
}
private static Expression BuildOrExpression(Expression existingExpression, Expression expressionToAdd)
{
if (existingExpression == null)
{
return expressionToAdd;
}
//Build 'OR' expression for each property
return Expression.OrElse(existingExpression, expressionToAdd);
}
}
Alternatively, take a look at the github project for NinjaNye.SearchExtensions as this has other options and has been refactored somewhat to allow other combinations
There is another, somewhat easier method that will accomplish this. ScottGu's blog details a dynamic linq library that I've found very helpful in the past. Essentially, it generates the query from a string you pass in. Here's a sample of the code you'd write:
Dim Northwind As New NorthwindDataContext
Dim query = Northwind.Products _
.Where("CategoryID=2 AND UnitPrice>3") _
.OrderBy("SupplierId")
Gridview1.DataSource = query
Gridview1.DataBind()
More info can be found at scottgu's blog here.
Either build an Expression<T> yourself, or look at a different route.
Assuming possibleTags is a collection of tags, you can make use of a closure and a join to find matches. This should find any songs with at least one tag in possibleTags:
allSongMatches = allSongMatches.Where(s => (select t from s.Tags
join tt from possibleTags
on t == tt
select t).Count() > 0)

Full Text Search in Linq

There's no full text search built into Linq and there don't seem to be many posts on the subject so I had a play around and came up with this method for my utlity class:
public static IEnumerable<TSource> GenericFullTextSearch<TSource>(string text, MyDataContext context)
{
//Find LINQ Table attribute
object[] info = typeof(TSource).GetCustomAttributes(typeof(System.Data.Linq.Mapping.TableAttribute), true);
//Get table name
String table = (info[0] as System.Data.Linq.Mapping.TableAttribute).Name;
//Full text search on that table
return context.ExecuteQuery<TSource>(String.Concat("SELECT * FROM ", table, " WHERE CONTAINS(*, {0})"), text);
}
And added this wrapper to each partial Linq class where there is a full text index
public static IEnumerable<Pet> FullTextSearch(string text, MyDataContext context)
{
return (LinqUtilities.GenericFullTextSearch<Pet>(text, context) as IEnumerable<Pet>);
}
So now I can do full text searches with neat stuff like
var Pets = Pet.FullTextSearch(helloimatextbox.Text, MyDataContext).Skip(10).Take(10);
I'm assuming only a very basic search is necessary at present. Can anyone improve on this? Is it possible to implement as an extension method and avoid the wrapper?
The neatest solution is to use an inline table valued function in sql and add it to your model
http://sqlblogcasts.com/blogs/simons/archive/2008/12/18/LINQ-to-SQL---Enabling-Fulltext-searching.aspx
To get it working you need to create a table valued function that does
nothing more than a CONTAINSTABLE query based on the keywords you
pass in,
create function udf_sessionSearch
(#keywords nvarchar(4000)) returns table as return (select [SessionId],[rank]
from containstable(Session,(description,title),#keywords))
You then add this function to your LINQ 2 SQL model and he presto you
can now write queries like.
var sessList = from s in DB.Sessions
join fts in DB.udf_sessionSearch(SearchText) on s.sessionId equals fts.SessionId
select s;
I was pretty frustrated with the lack of clear examples... especially when there are potentially large data sets and paging is needed. So, here's an example that hopefully encompasses everything you might need :-)
create function TS_projectResourceSearch
( #KeyStr nvarchar(4000),
#OwnId int,
#SkipN int,
#TakeN int )
returns #srch_rslt table (ProjectResourceId bigint not null, Ranking int not null )
as
begin
declare #TakeLast int
set #TakeLast = #SkipN + #TakeN
set #SkipN = #SkipN + 1
insert into #srch_rslt
select pr.ProjectResourceId, Ranking
from
(
select t.[KEY] as ProjectResourceId, t.[RANK] as Ranking, ROW_NUMBER() over (order by t.[Rank] desc) row_num
from containstable( ProjectResource,(ResourceInfo, ResourceName), #KeyStr )
as t
) as r
join ProjectResource pr on r.ProjectResourceId = pr.ProjectResourceId
where (pr.CreatorPersonId = #OwnId
or pr.ResourceAvailType < 40)
and r.row_num between #SkipN and #TakeLast
order by r.Ranking desc
return
end
go
select * from ts_projectResourceSearch(' "test*" ',1002, 0,1)
Enjoy,
Patrick
I use a little hack using Provider Wrapper techniques. I have a c# code that rewrite magic word in SQL with FTS search for MS SQL (you can adjust for any server you like).
if you have context class MyEntities, create subclass like
public class MyEntitiesWithWrappers : MyEntities
{
private IEFTraceListener listener;
public string FullTextPrefix = "-FTSPREFIX-";
public MyEntitiesWithWrappers(): this("name=MyEntities")
{
}
public MyEntitiesWithWrappers(string connectionString)
: base(EntityConnectionWrapperUtils.CreateEntityConnectionWithWrappers(connectionString,"EFTracingProvider"))
{
TracingConnection.CommandExecuting += RewriteFullTextQuery;
}
/// <summary>
/// Rewrites query that contains predefined prefix like: where n.NOTETEXT.Contains(Db.FullTextPrefix + text) with SQL server FTS
/// To be removed when EF will support FTS
/// </summary>
/// <param name="o"></param>
/// <param name="args"></param>
public void RewriteFullTextQuery(object o, CommandExecutionEventArgs args)
{
var text = args.Command.CommandText;
for (int i = 0; i < args.Command.Parameters.Count; i++)
{
DbParameter parameter = args.Command.Parameters[i];
if (parameter.DbType.In(DbType.String, DbType.AnsiString, DbType.StringFixedLength, DbType.AnsiStringFixedLength))
{
if (parameter.Value == DBNull.Value)
continue;
var value = (string) parameter.Value;
parameter.Size = 4096;
if (value.IndexOf(FullTextPrefix) >= 0)
{
value = value.Replace(FullTextPrefix, ""); // remove prefix we added n linq query
value = value.Substring(1, value.Length-2); // remove %% escaping by linq translator from string.Contains to sql LIKE
parameter.Value = value;
args.Command.CommandText = Regex.Replace(text,
string.Format(#"\(\[(\w*)\].\[(\w*)\]\s*LIKE\s*#{0}\s?(?:ESCAPE '~')\)", parameter.ParameterName),
string.Format(#"contains([$1].[$2], #{0})", parameter.ParameterName));
}
}
}
}
}
And then use it like this:
var fullTextSearch = Db.FullTextPrefix + textToSearch;
var q = Db.Notes.Where(n => !n.Private && n.NoteText.Contains(fullTextSearch));
A slighty nicer method (takes rank into effect) using CONTAINSTABLE
String pkey = context.Mapping.GetTable(typeof(TSource)).RowType.DataMembers.SingleOrDefault(x => x.IsPrimaryKey).Name;
string query = String.Concat(#"SELECT *
FROM ", table, #" AS FT_TBL INNER JOIN
CONTAINSTABLE(", table, #", *, {0}) AS KEY_TBL
ON FT_TBL.", pkey, #" = KEY_TBL.[KEY]
ORDER BY KEY_TBL.[RANK] DESC");
return context.ExecuteQuery<TSource>(query, text);
.NET Core 2.1 and above supports an extension method that allows the use of FREETEXT and FREETEXTTABLE searches
using Microsoft.EntityFrameworkCore;
var results = dbContext.MyTable
.Where(e => EF.Functions.FreeText("*", "search criteria"));
The FreeText function is defined in Microsoft.EntityFrameworkCore.SqlServer so your project must reference that package.
Documentation
I've been trying to solve the exact problem. I like to write my SQL logic in my LINQtoSQL but I needed a way to do Full Text Search. right now I'm just using SQL functions and then calling the user-defined functions inline of the linq queries. not sure if that's the most efficient way. what do you guys think?
You can just do something like this
var results = (from tags in _dataContext.View_GetDeterminationTags
where tags.TagName.Contains(TagName) ||
SqlMethods.Like(tags.TagName,TagName)
select new DeterminationTags
{
Row = tags.Row,
Record = tags.Record,
TagID = tags.TagID,
TagName = tags.TagName,
DateTagged = tags.DateTagged,
DeterminationID = tags.DeterminationID,
DeterminationMemberID = tags.DeterminationMemberID,
MemberID = tags.MemberID,
TotalTagged = tags.TotalTagged.Value
}).ToList();
Notice where TagName.Contains also the SQLMethods.Like just do a using
using System.Data.Linq.SqlClient;
to gain access to that SQLMethods.
dswatik - the reason for wanting full text search is that .contains translates to
SELECT * FROM MYTABLE WHERE COLUMNNAME LIKE '%TEXT%'
Which ignores any indexes and is horrible on a large table.

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