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Linq query parameterised operator and column name [duplicate]

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C# Dynamic database filtering with Linq Expression
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I am looking to implement a system whereby a use that 'build' conditions and then return the resulting data back from the database. At present, there is a stored procedure which generates SQL on the fly and executes it. This is a particular issue that I want to remove.
My problem is coming from the fact that I can have multiple fields within my criteria, and for each of these fields, there could be 1 or more values, with different potential operators.
For example,
from t in Contacts
where t.Email == "email#domain.com" || t.Email.Contains ("mydomain")
where t.Field1 == "valuewewant"
where t.Field2 != "valuewedontwant"
select t
The field, criteria and operator are stored in the database (and List<FieldCriteria>) and would be some thing like this (based on above);
Email, Equals, "email#domain.com"
Email, Contains, "mydomain" Field1,
Equals, "valuewewant" Field2,
DoesNotEqual, "valuewedontwant"
or
new FieldCriteria
{
FieldName = "Email",
Operator = 1,
Value = "email#mydomain.com"
}
So using the information that I have, I want to be able to build a query with any number of conditions. I have seen previous links to Dynamic Linq and PredicateBuilder, but am not able to visualise this as a solution to my own problem.
Any suggestions would be appreciated.
Update
Following on from the suggestion about Dynamic Linq, I came up with a very basic solution, using a Single Operator, with 2 Fields and multiple Criteria. A little crude at the moment as coded in LinqPad, but the results are exactly what I wanted;
enum Operator
{
Equals = 1,
}
class Condition
{
public string Field { get; set; }
public Operator Operator { get; set;}
public string Value { get; set;}
}
void Main()
{
var conditions = new List<Condition>();
conditions.Add(new Condition {
Field = "Email",
Operator = Operator.Equals,
Value = "email1#domain.com"
});
conditions.Add(new Condition {
Field = "Email",
Operator = Operator.Equals,
Value = "email2#domain.com"
});
conditions.Add(new Condition {
Field = "Field1",
Operator = Operator.Equals,
Value = "Chris"
});
var statusConditions = "Status = 1";
var emailConditions = from c in conditions where c.Field == "Email" select c;
var field1Conditions = from c in conditions where c.Field == "Field1" select c;
var emailConditionsFormatted = from c in emailConditions select string.Format("Email=\"{0}\"", c.Value);
var field1ConditionsFormatted = from c in field1Conditions select string.Format("Field1=\"{0}\"", c.Value);
string[] conditionsArray = emailConditionsFormatted.ToArray();
var emailConditionsJoined = string.Join("||", conditionsArray);
Console.WriteLine(String.Format("Formatted Condition For Email: {0}",emailConditionsJoined));
conditionsArray = field1ConditionsFormatted.ToArray();
var field1ConditionsJoined = string.Join("||", conditionsArray);
Console.WriteLine(String.Format("Formatted Condition For Field1: {0}",field1ConditionsJoined));
IQueryable results = ContactView.Where(statusConditions);
if (emailConditions != null)
{
results = results.Where(emailConditionsJoined);
}
if (field1Conditions != null)
{
results = results.Where(field1ConditionsJoined);
}
results = results.Select("id");
foreach (int id in results)
{
Console.WriteLine(id.ToString());
}
}
With an SQL generated of;
-- Region Parameters
DECLARE #p0 VarChar(1000) = 'Chris'
DECLARE #p1 VarChar(1000) = 'email1#domain.com'
DECLARE #p2 VarChar(1000) = 'email2#domain.com'
DECLARE #p3 Int = 1
-- EndRegion
SELECT [t0].[id]
FROM [Contacts].[ContactView] AS [t0]
WHERE ([t0].[field1] = #p0) AND (([t0].[email] = #p1) OR ([t0].[email] = #p2)) AND ([t0].[status] = #p3)
And Console Output:
Formatted Condition For Email: Email="email1#domain.com"||Email="email2#domain.com"
Formatted Condition For Field1: Field1="Chris"
Just need clean this up and add the other Operators and it is looking good.
If anyone has any comments on this so far, any input would be appreciated

The trick with LINQ would be to build an Expression from the data. As an example, to illustrate the example shown:
var param = Expression.Parameter(typeof(MyObject), "t");
var body = Expression.Or(
Expression.Equal(Expression.PropertyOrField(param, "Email"), Expression.Constant("email#domain.com")),
Expression.Call(Expression.PropertyOrField(param, "Email"), "Contains", null, Expression.Constant("mydomain"))
);
body = Expression.AndAlso(body, Expression.Equal(Expression.PropertyOrField(param, "Field1"), Expression.Constant("valuewewant")));
body = Expression.AndAlso(body, Expression.NotEqual(Expression.PropertyOrField(param, "Field2"), Expression.Constant("valuewedontwant")));
var lambda = Expression.Lambda<Func<MyObject, bool>>(body, param);
var data = source.Where(lambda);
In particular, note how AndAlso can be used to compose the various operations (the same as multiple Where, but simpler).

I think Dynamic LINQ will be one of option. DLINQ allows you to specify part of the LINQ query as "string" and DLINQ then compiles that string to Expression tree so that be passed to the underlying LINQ provider. Your need is also same i.e you need to create Expression trees at runtime.
I would suggest you to make the property Operator in FieldCriteria as an Enum which represent all the required operations (equals, less then etc). Then you will need to write a function that takes a list of FieldCriteria and return a "expression" string which then can be fed into DLINQ to get the expression tree.

This sounds very similar to a problem I solved recently. In my case, I had to filter the objects into different categories based on a complex filters that were defined in Sql.
I have created a Nuget package DynamicFilter.Sql to dynamically generate the lambda expression from a sql based filter. The package is open source and available on github.
you can simply use it like so,
var filter = FilterExpression.Compile<User>("(Email = 'email#domain.com' or Email like '%#%mydomain.com') and deleted <> true ");
bool match = filter(new User {Email="alice#mydomain.com", Deleted=false}); //Matches true

This can be simply done by Linq where you attach additional operators to the query object. Here is an example.
query = db.Contacts.Where( ... );
query = query.Where( ... );
query = query.Where( ... );
This is a more simpler and short solution.

Passing parameter to LINQ query

I have a method like below:
public void GetUserIdByCode(string userCode)
{
var query = from u in db.Users
where u.Code == userCode // userCode = "LRAZAK"
select u.Id;
var userId = query.FirstOrDefault(); // userId = 0 :(
}
When I ran the code, I got the default value of 0 assigned to userId meaning the Id was not found.
However, if I changed the userCode with a string like below, I will get the value I want.
public void GetUserIdByCode(string userCode)
{
var query = from u in db.Users
where u.Code == "LRAZAK" // Hard-coded string into the query
select u.Id;
var userId = query.FirstOrDefault(); // userId = 123 Happy days!!
}
My question is why passing the parameter into the LINQ query does not work?
When I stepped into the code, I got the SQL statement like so:
// Does not work...
{SELECT "Extent1"."LOGONNO" AS "LOGONNO"FROM "DEBTORSLIVE"."DEBTORS_LOGONS" "Extent1"WHERE ("Extent1"."LOGONCODE" = :p__linq__0)}
The hard-coded LINQ query (the working one) gives an SQL statement as below:
// Working just fine
{SELECT "Extent1"."LOGONNO" AS "LOGONNO"FROM "DEBTORSLIVE"."DEBTORS_LOGONS" "Extent1"WHERE ('LRAZAK' = "Extent1"."LOGONCODE")}
What would be the solution?

As a work-around, I use Dynamic Linq.
The code below is working for me.
public void GetUserIdByCode(string userCode)
{
string clause = String.Format("Code=\"{0}\"", userCode);
var userId = db.Users
.Where(clause)
.Select(u => u.Id)
.FirstOrDefault();
}
The database query returns an object of User with Code and Id as properties. This is defined in one of my classes.

Here is syntax that will work to pass an argument to a LINQ query.
Not sure how many people will be searching this topic so many years later, but here's a code example that gets the job done:
string cuties = "777";
// string collection
IList<string> stringList = new List<string>() {
"eg. 1",
"ie LAMBDA",
"777"
};
var result = from s in stringList
where (s == cuties)
select s;
foreach (var str in result)
{
Console.WriteLine(str); // Output: "777"
}

Subquery using LINQ to SQL

I am using LINQ to SQL in my C# tutorial project but I have basic knowledge of it.
I made a SQL query like this:
SELECT ID,HeroName,HeroRarity,Initiative,Attack,Attack1
FROM CharactersName
WHERE ID IN(
SELECT HeroID
FROM Hero_Group
WHERE GroupID=1
)
(Hero_Group) is a table to deal with a many-to-many relation between (CharactersName) table and another table named (Groups) where a character can be in more than one group.
I tried to write it in LINQ like this:
void FilterGroup()
{
HDAEntities db = new HDAEntities();
var query = from obj in db.CharactersNames
where obj.ID == from obj2 in db.Hero_Group
where obj2.GroupID == comboBox1.SelectedIndex
select new
{
obj2.GroupID
}
select new
{
obj.ID,
obj.HeroName,
obj.HeroRarity,
obj.Initiative,
obj.Attack,
obj.Attack1
};
}
But of course this is gibberish.
Can someone help me, please ? (be informed that I have little knowledge of LINQ to SQL)
~TIA~

You can do it like this:
void FilterGroup()
{
HDAEntities db = new HDAEntities();
var subQuery = db.Hero_Group.Where(h => h.GroupID == comboBox1.selectedIndex)
.Select(h => h.GroupID);
var query = from obj in db.CharactersNames
where subQuery.Contains(obj.ID)
select new
{
obj.ID,
obj.HeroName,
obj.HeroRarity,
obj.Initiative,
obj.Attack,
obj.Attack1
};
var result = query.ToList(); // this is where your query and subquery are evaluated and sent to the database
db.Dispose();
db = null;
}
Note that the subQuery is not evaluated until you call ToList(). You also need to dispose the object (or try the using statement to create the HDAEntities object). Also, make sure you don't dispose the db before evaluating the query (calling ToList after Dispose will throw an exception).

var query = from obj in db.CharactersNames
where (from obj2 in db.Hero_Group
where obj2.GroupID == comboBox1.SelectedIndex
select new {obj2.GroupID}).Contains(obj.ID)
select new
{
obj.ID,
obj.HeroName,
obj.HeroRarity,
obj.Initiative,
obj.Attack,
obj.Attack1
};

var query = from obj in db.CharactersNames
where (from obj2 in db.Hero_Group
where obj2.GroupID == comboBox1.SelectedIndex
select new {obj2.GroupID}).Contains(obj.ID)
select new
{
obj.ID,
obj.HeroName,
obj.HeroRarity,
obj.Initiative,
obj.Attack,
obj.Attack1
};

Adding a where/order by clause to an IQueryable

I have ths function to query a set of records from the DB:
public IQueryable<PointTransactionViewModel> GetPointTransactions(int UserID)
{
return
(
from PointTransaction p in entities.PointTransaction
join ActivityLog a in entities.ActivityLog
on p.TransactionID equals a.TransactionID
where p.UserID == UserID
select new PointTransactionViewModel
{
ID = p.TransactionID,
Balance = p.Balance,
Points = p.Amount,
RelatedActivityID = a.ID,
When = p.When,
Sender = p.SenderUserInfo.CompleteName
}
);
}
I wish to add an additional cause, like this
var entries = GetPointTransaction(1);
return entries.OrderbyDescending.Where( x => x.When >= start && w.When <= end).
( x => x.When);
However, I seem to need to create a new query from the existing one for this to work. But, I have seem this work before without creating a new query, in the code snippet before:
public PaginatedList(IQueryable<T> source, int pageIndex, int pageSize)
{
PageIndex = pageIndex;
PageSize = pageSize;
TotalCount = source.Count();
TotalPages = (int)Math.Ceiling(TotalCount / (double)PageSize);
this.AddRange(source.Skip(PageIndex * PageSize).Take(PageSize));
}
Does the code above somehow doesn't need a new query to be created for the IQueryable source object? Was a temporary object created?
Edit
It's strange, but to get it to work I have to do the following:
IQueryable<ActivityLogEntry> log = activityRepo.GetPointTransaction(userID).
Where(x => x.PointsEarned == 50);
return log.ToList();
The following will not work:
var log = = activityRepo.GetPointTransaction(userID);
log.Where( x => x.PointsEarned == 50);
return log.ToList();
There is no error message, just that the where clause seems to be ignored (it is also returning all data which PointsEarned is not 50)

Your entries is of IQueryable type, that's enough and you can add any number of clauses before fetching the data, e.g. before calling the ToList() function.
It doesn't execute the SQL code, just an expression tree will be created until you fetch the whole data with one of the existing methods (again, e.g. the ToList() function).
var query = context.Where(x=>x.id == test);
query = query.Where(anotherCondition1);
query = query.Where(anotherCondition2);
...
var result = query.ToList();
it's equal to
var result = context.Where(x=>x.id == test)
.Where(anotherCondition1)
.Where(anotherCondition2)
....
.ToList()
This is called deferred execution, for more details see the MSDN blog post on LINQ and Deferred Execution.

You do need to create a new object. IQueryable is immutable. Don't worry this is how you are supposed to do it. This is how the queries are formed internally. All the extension methods like "Where" don't actually change the object. They just return a new one.
The code that you claim works should not work. The method doesn't even have a type.

i mean you can write this sample :
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));
}
//------Other Condition you need
if(!String.IsNullOrEmpty(title))
{
opportunites = opportunites.Where(.....);
}
if(!String.IsNullOrEmpty(name))
{
opportunites = opportunites.Where(.....);
}

As others have pointed out, you do not need a new object. Your syntax for OrderByDescending is wrong though, you need to specify the key selector.
var entries = GetPointTransaction(1);
return entries.Where(x => x.When >= start && w.When <= end).OrderbyDescending(x => x.When);

String.Split in a Linq-To-SQL Query?

I have a database table that contains an nvarchar column like this:
1|12.6|18|19
I have a Business Object that has a Decimal[] property.
My LINQ Query looks like this:
var temp = from r in db.SomeTable select new BusinessObject {
// Other BusinessObject Properties snipped as they are straight 1:1
MeterValues = r.MeterValues.Split('|').Select(Decimal.Parse).ToArray()
};
var result = temp.ToArray();
This throws an NotSupportedException: Method 'System.String[] Split(Char[])' has no supported translation to SQL.
That kinda sucks :) Is there any way I can do this without having to add a string property to the business object or selecting an anonymous type and then iterating through it?
My current "solution" is:
var temp = from r in db.SomeTable select new {
mv = r.MeterValues,
bo = new BusinessObject { // all the other fields }
};
var result = new List<BusinessObject>();
foreach(var t in temp) {
var bo = t.bo;
bo.MeterValues = t.mv.Split('|').Select(Decimal.Parse).ToArray();
result.Add(bo);
}
return result.ToArray(); // The Method returns BusinessObject[]
That's kinda ugly though, with that temporary list.
I've tried adding a let mv = r.MeterValues.Split('|').Select(Decimal.Parse).ToArray() but that essentially leads to the same NotSupportedException.
This is .net 3.5SP1 if that matters.

You need to force the select clause to run on the client by calling .AsEnumerable() first:
var result = db.SomeTable.AsEnumerable().Select(r => new BusinessObject {
...
MeterValues = r.MeterValues.Split('|').Select(Decimal.Parse).ToArray()
}).ToList();

You can't use split, but in this scenario you can do the following:
// Database value is 1|12.6|18|19
string valueToFind = "19";
var temp = from r in db.SomeTable.Where(r => ("|" + r.MeterValues + "|").Contains("|" + valueToFind + "|"));
This code adds outer pipes (|) to the database value on the fly inside the query so you can do start, middle, and end value matches on the string.
For example, the above code looks for "|19|" inside "|1|12.6|18|19|", which is found and valid. This will work for any other valueToFind.

You don't need to use a temporary list:
var query = from r in db.SomeTable
select new
{
r.Id,
r.Name,
r.MeterValues,
...
};
var temp = from x in query.AsEnumerable()
select new BusinessObject
{
Id = x.Id,
Name = x.Name,
MeterValues = x.mv.Split('|').Select(Decimal.Parse).ToArray(),
...
};
return temp.ToArray();

Unfortunately its the IQueryable you are using (Linq to SQL) that is not supporting the Split function.
You are really only left with the IEnumerable (Linq to Objects) support for it in this case. You second code snippet is what you need to do, or something like...
var temp = (from r in db.SomeTable select new {
mv = r.MeterValues,
bo = new BusinessObject { // all the other fields }
}).AsEnumerable().Select(blah, blah) ;