I am using Linq-to-SQL.
Currently I am binding gridview through linq which query written in business logic call. I have extract record through query in business logic class and I want to bind that particular data to gridview and return data.
How to return data which type is array?
The code is here:
CMSBusiness.DataClasses1DataContext db = new DataClasses1DataContext();
var cate =
from p in db.categoryTables
select new
{
categoryId=p.categoryId,
categoryName=p.categoryName,
categoryDesc=p.categoryDesc
};
How to return value and bind gridview?
Try gridView.DataSource = cate;, this should work.
We also recommend you to take a look at this article.
Related
I want to execute the following select:
SELECT 0 as Value
What is the correlating syntax in LINQ for SQL?
Edit
I want to use the correlating LINQ for SQL statement in a Concat() call like this
var c = (from a in mytable select a.Value).Concat(select 0).Sum();
As you can see, Concat(select 0) obviously doesn't compile. Any ideas?
Edit 2
David suggested to use a simple collection instead. I've tried
private decimal[] mZeroDecimals = new[] { 0.0m };
...
public void MyFunction()
{
var c = (from a in mytable select a.Value).Concat(mZeroDecimals).Sum();
...
but it throws an exception Local sequence cannot be used in LINQ to SQL implementation of query operators except the Contains() operator.
You're not actually querying anything, so there is no LINQ involved. You're just creating an anonymous object with a single property called Value:
var obj = new { Value = 0 };
Edit: Based on your comment, it sounds like you want this object in a collection. That doesn't make it a LINQ query (since you're still not querying anything), but you can declare a collection just as easily as a single object. Something like this:
var coll = new[] { new { Value = 0 } };
Since this is a collection, it can be used with any of the enumerable extension methods that LINQ uses, which sounds like what you're trying to do.
I would like to query a table based on a list of KeyValuePair. With a Model-First approach, I could do the following:
var context = new DataContext();
var whereClause = new StringBuilder();
var objectParameters = new List<ObjectParameter>();
foreach(KeyValuePair<string, object> pair in queryParameters)
{
if (whereClause.Length > 0)
whereClause.Append(" AND ");
whereClause.Append(string.Format("it.[{0}] = #{0}", pair.Key));
parameters.Add(new ObjectParameter(pair.Key, pair.Value));
}
var result = context.Nodes.Where(whereClause.ToString(), parameters.ToArray());
Now I'm using a Code-First approach and this Where method is not available anymore. Fortunately, I saw an article somewhere (I can't remember anymore) which suggested that I could convert the DbContext to a IObjectContextAdapter then call CreateQuery like this:
var result = ((IObjectContextAdapter)context)
.ObjectContext.CreateQuery<Node>(whereClause.ToString(), parameters.ToArray());
Unfortunately, this throws an error:
'{ColumnName}' could not be resolved in the current scope or context. Make sure that all referenced variables are in scope, that required schemas are loaded, and that namespaces are referenced correctly.
Where {ColumnName} is the column specified in the whereClause.
Any ideas how I can dynamically query a DbSet given a list of key/value pairs? All help will be greatly appreciated.
I think your very first problem is that in the first example you are using Where on the entity set but in the second example you are using CreateQuery so you must pass full ESQL query and not only where clause! Try something like:
...
.CreateQuery<Node>("SELECT VALUE it FROM ContextName.Nodes AS it WHERE " + yourWhere)
The most problematic is full entity set name in FROM part. I think it is defined as name of the context class and name of the DbSet exposed on the context. Another way to do it is creating ObjectSet:
...
.ObjectContext.CreateObjectSet<Node>().Where(yourWhere)
I'm trying to select an object using values of another object in LINQ SQL,
I currently have this,
var result1 = (from s in pdc.ScanLogs
from ec in pdc.ExhibitsContacts
where s.ExhibitID == ec.ExhibitID
select ec.Contact);
I want to assign a value of ec.Contact.Note = ec.Comment;
Is there to a way to do this in LINQ SQL without writing multiple queries?
I read this blog article: http://blog.robvolk.com/2009/05/linq-select-object-but-change-some.html but it doesn't seem to work with LINQ SQL.
Basically you can't do this. LINQ is meant to be a query language, and what you want to do is mutate existing entities with your query. This means your query would have side effects and this is not something that is supported by LINQ to SQL.
While this won't work in a single query while returning LINQ to SQL entities, what will work is when you return simple DTO structues. For instance:
var result1 =
from s in pdc.ScanLogs
from ec in s.ExhibitsContacts
select new ContactDto
{
Id = ec.Contact.Id,
Note = ec.Comment,
SomeOtherFields = ec.Contact.SomeOtherFields
};
As a side note: also look at how I removed the where s.ExhibitID == ec.ExhibitID join from the query, by just using the ExhibitsContacts property of the ScanLog entity (which will be generated by LINQ to SQL for you when your database schema has the proper foreign keys defined).
Update:
When you need to return those DTO from several methods, you might consider centralizing the transformation from a collection of entities to a collection of DTO objects. What I tend to do is place this method on the DTO (which makes it easy to find). The code might look like this:
public class ContactDto
{
// Many public properties here
public static IQueryable<ContactDto> ToDto(
IQueryable<Contact> contacts)
{
return
from contact in contacts
select new ContactDto
{
Id = contact.Id,
Note = contact.ExhibitsContact.Comment,
ManyOtherFields = contact.ManyOtherFields
};
}
}
The trick with this static transformation method is that it takes an IQueryable and returns an IQueryable. This allows to to simply specify the transformation and let LINQ to SQL (or any other LINQ enabled O/RM) to efficiently execute that LINQ expression later on. The original code would now look like this:
IQueryable<Contact> contacts =
from s in pdc.ScanLogs
from ec in s.ExhibitsContacts
select ec.Contact;
IQuerable<ContactDto> result1 = ContactDto.ToDto(contacts);
the problem is that LINQ to SQL does not know how to interpret your extension method. The only way, other than using stored procedures from LINQ to SQL (which kind of defeats the ponit), is to get the object, update and then commit changes.
I am trying to get the records from the 'many' table of a one-to-many relationship and add them as a list to the relevant record from the 'one' table.
I am also trying to do this in a single database request.
Code derived from Linq to Sql - Populate JOIN result into a List almost achieves the intended result, but makes one database request per entry in the 'one' table which is unacceptable. That failing code is here:
var res = from variable in _dc.GetTable<VARIABLE>()
select new { x = variable, y = variable.VARIABLE_VALUEs };
However if I do a similar query but loop through all the results, then only a single database request is made. This code achieves all goals:
var res = from variable in _dc.GetTable<VARIABLE>()
select variable;
List<GDO.Variable> output = new List<GDO.Variable>();
foreach (var v2 in res)
{
List<GDO.VariableValue> values = new List<GDO.VariableValue>();
foreach (var vv in v2.VARIABLE_VALUEs)
{
values.Add(VariableValue.EntityToGDO(vv));
}
output.Add(EntityToGDO(v2));
output[output.Count - 1].VariableValues = values;
}
However the latter code is ugly as hell, and it really feels like something that should be do-able in a single linq query.
So, how can this be done in a single linq query that makes only a single database query?
In both cases the table is set to preload using the following code:
_dc = _db.CreateLinqDataContext();
var loadOptions = new DataLoadOptions();
loadOptions.LoadWith<VARIABLE>(v => v.VARIABLE_VALUEs);
_dc.LoadOptions = loadOptions;
I am using .NET 3.5, and the database back-end was generated using SqlMetal.
This link may help
http://msdn.microsoft.com/en-us/vcsharp/aa336746.aspx
Look under join operators. You'll probably have to change from using extension syntax other syntax too. Like this,
var = from obj in dc.Table
from obj2 in dc.Table2
where condition
select
I need to translate the following Code to an Expression and I will explain why:
results = results.Where(answer => answer.Question.Wording.Contains(term));
results is IQueryable<ISurveyAnswer>
Question is ISurveyQuestion
Wording is String
The problem is, Question is not always the name of the LINQ to SQL property.
This will give me the PropertyInfo for the actual ISurveyQuestion property
private static PropertyInfo FindNaturalProperty<TMemberType>(Type search)
{
IDictionary<string,PropertyInfo> properties = new Dictionary<string,PropertyInfo>();
search.GetProperties().Each(prop =>
{
if (null != prop.PropertyType.GetInterface(typeof(TMemberType).Name))
properties.Add(prop.Name, prop);
});
if (properties.Count < 1) throw new ArgumentException(String.Format("{0} has no properties of type {1}", search.Name, typeof(TMemberType).Name));
if (properties.Count == 1) return properties.Values.First();
search.GetInterfaces().Each(inter =>
{
inter.GetProperties().Each(prop =>
{
if (null != prop.PropertyType.GetInterface(typeof(TMemberType).Name))
properties.Remove(prop.Name);
});
});
if (properties.Count < 1) throw new ArgumentException(String.Format("{0} has no properties of type {1} that are not members of an interface", search.Name, typeof(TMemberType).Name));
if (properties.Count > 1) throw new AmbiguousMatchException(String.Format("{0} has more than one property that are of type {1} and are not members of an interface", search.Name, typeof(TMemberType).Name));
return properties.Values.First();
}
Once I have the PropertyInfo how do I translate that to an Expression Tree?
EDIT:
What I basically need is:
results = results.Where(answer => answer.GetQuestionProperty().GetValue(answer).Wording.Contains(term));
But that doesn't work so I need to build the Expression Tree myself, for linq-to-sql.
Reading the question I think what you're after is Dynamic Linq - which is a helper library to let you build Linq queries dynamically (!) using strings as opposed to at design time. That means that if you can get your property name you should be able create your query on the fly.
ScottGu has an article here
What your trying to do is create a dynamic query and you want the action tables / properties your query against to be dynamic as well. I am not sure if this is easily possible based on how you want to use it.
Check out ScottGu's blog post:
http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx
and
Check out Rick Strahl's blog post:
http://www.west-wind.com/Weblog/posts/143814.aspx
http://www.linqpad.net/
linqpad will convert it for you.