Dynamic Linq creation - sql

I am re-writing a query which is created in response to user's entry into text fields in order to offer some protection against SQL injection attack.
SELECT DISTINCT (FileNameID) FROM SurNames WHERE Surname IN
('Jones','Smith','Armitage')
AND FileNameID IN ( SELECT DISTINCT (FileNameID) FROM FirstNames WHERE FirstName
IN ('John','William') )
There can be up to 3 other tables involved in this process.
The parameter lists can be up to 50-100 entries so building a parameterized query is tedious and cumbersome.
I am trying to create a Linq query which should take care of the parameterization and offer the protection I need.
This gives me what I need
var surnameValues = new[] { "Jones","Smith","Armitage" };
var firstnameValues = new[] { "John","William" };
var result = (from sn in db.Surnames
from fn in db.FirstNames
where surnameValues.Contains(sn.Surname) &&
firstnameValues.Contains(fn.FirstName)
select fn.FileNameID).Distinct().ToArray();
I now need a way to dynamically create this depending upon whether the user has selected/entered values in the surname or firstname text entry boxes?
Any pointers will be gratefully received
Thanks
Roger

you could combine all the logic into the query;
var surnameValues = new[] { "Jones","Smith","Armitage" };
var firstnameValues = null;
// Set these two variables to handle null values and use an empty array instead
var surnameCheck= surnameValues ?? new string[0];
var firstnameCheck= firstnameValus ?? new string[0];
var result = (from sn in db.Surnames
from fn in db.FirstNames
where
(!surnameCheck.Any() || surnameCheck.Contains(sn.Surname)) &&
(!firstnameCheck.Any() || firstnameCheck.Contains(fn.FirstName))
select fn.FileNameID).Distinct().ToArray();
Your query doesn't seem to have a join condition betwwen the Surnames table and the firstNames table?
You could dynamically build the query (as you appear to be doing I cross join I've used SelectMany)
var query=db.Surnames.SelectMany(sn=>db.FirstNames.Select (fn => new {fn=fn,sn=sn}));
if (surnameValues!=null && surnameValues.Any()) query=query.Where(x=>surnameValues.Contains(x.sn.Surname));
if (firstnameValues !=null && firstnameValues.Any()) query=query.Where(x=>firstnameValues.Contains(x.fn.FirstName));
var result=query.Select(x=>x.fn.FileNameID).Distinct();

Related

Is there unpivot or cross apply in ServiceStack ormlite?

I am using ServiceStack 4.5.14. I want to pass a list of Guid to such as below query.
Table Name: Image
Columns: (Id -> Type=Guid) (ImageId -> Type=Guid) (Guid -> Type=Guid)
var result = Db.ExecuteSql("select value from image unpivot (value for col in (Id, ImageId)) un where Guid=(#param) order by Guid",
new { param = "5de7f247-f590-479a-9c29-2e68a57e711c" });
It returns a result which their Id and ImageId are 000.... while they are null.
Another question is: how can I send a list of Guid as parameter to above query?
To query a parameterized field you should include the Guid instead of the string, e.g:
var result = Db.ExecuteSql(
#"select value from image unpivot (value for col in (Id, ImageId)) un
where Guid=(#param) order by Guid",
new { param = new Guid("5de7f247-f590-479a-9c29-2e68a57e711c") });
If values are null, it's likely masquerading an error, you can bubble errors with:
OrmLiteConfig.ThrowOnError = true;
Or enable debug logging with:
LogManager.LogFactory = new ConsoleLogFactory();
In v5+ you can also inspect SQL commands before they're executed with:
OrmLiteConfig.BeforeExecFilter = dbCmd => Console.WriteLine(dbCmd.GetDebugString());

Getting Custom Column from IQueryable DB First Approach EF

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;
}

Entity Framework filter data by string sql

I am storing some filter data in my table. Let me make it more clear: I want to store some where clauses and their values in a database and use them when I want to retrieve data from a database.
For example, consider a people table (entity set) and some filters on it in another table:
"age" , "> 70"
"gender" , "= male"
Now when I retrieve data from the people table I want to get these filters to filter my data.
I know I can generate a SQL query as a string and execute that but is there any other better way in EF, LINQ?
One solution is to use Dynamic Linq Library , using this library you can have:
filterTable = //some code to retrive it
var whereClause = string.Join(" AND ", filterTable.Select(x=> x.Left + x.Right));
var result = context.People.Where(whereClause).ToList();
Assuming that filter table has columns Left and Right and you want to join filters by AND.
My suggestion is to include more details in the filter table, for example separate the operators from operands and add a column that determines the join is And or OR and a column that determines the other row which joins this one. You need a tree structure if you want to handle more complex queries like (A and B)Or(C and D).
Another solution is to build expression tree from filter table. Here is a simple example:
var arg = Expression.Parameter(typeof(People));
Expression whereClause;
for(var row in filterTable)
{
Expression rowClause;
var left = Expression.PropertyOrField(arg, row.PropertyName);
//here a type cast is needed for example
//var right = Expression.Constant(int.Parse(row.Right));
var right = Expression.Constant(row.Right, left.Member.MemberType);
switch(row.Operator)
{
case "=":
rowClause = Expression.Equal(left, right);
break;
case ">":
rowClause = Expression.GreaterThan(left, right);
break;
case ">=":
rowClause = Expression.GreaterThanOrEqual(left, right);
break;
}
if(whereClause == null)
{
whereClause = rowClause;
}
else
{
whereClause = Expression.AndAlso(whereClause, rowClause);
}
}
var lambda = Expression.Lambda<Func<People, bool>>(whereClause, arg);
context.People.Where(lambda);
this is very simplified example, you should do many validations type casting and ... in order to make this works for all kind of queries.
This is an interesting question. First off, make sure you're honest with yourself: you are creating a new query language, and this is not a trivial task (however trivial your expressions may seem).
If you're certain you're not underestimating the task, then you'll want to look at LINQ expression trees (reference documentation).
Unfortunately, it's quite a broad subject, I encourage you to learn the basics and ask more specific questions as they come up. Your goal is to interpret your filter expression records (fetched from your table) and create a LINQ expression tree for the predicate that they represent. You can then pass the tree to Where() calls as usual.
Without knowing what your UI looks like here is a simple example of what I was talking about in my comments regarding Serialize.Linq library
public void QuerySerializeDeserialize()
{
var exp = "(User.Age > 7 AND User.FirstName == \"Daniel\") OR User.Age < 10";
var user = Expression.Parameter(typeof (User), "User");
var parsExpression =
System.Linq.Dynamic.DynamicExpression.ParseLambda(new[] {user}, null, exp);
//Convert the Expression to JSON
var query = e.ToJson();
//Deserialize JSON back to expression
var serializer = new ExpressionSerializer(new JsonSerializer());
var dExp = serializer.DeserializeText(query);
using (var context = new AppContext())
{
var set = context.Set<User>().Where((Expression<Func<User, bool>>) dExp);
}
}
You can probably get fancier using reflection and invoking your generic LINQ query based on the types coming in from the expression. This way you can avoid casting the expression like I did at the end of the example.

Does Dapper support the like operator?

Using Dapper-dot-net...
The following yields no results in the data object:
var data = conn.Query(#"
select top 25
Term as Label,
Type,
ID
from SearchTerms
WHERE Term like '%#T%'",
new { T = (string)term });
However, when I just use a regular String Format like:
string QueryString = String.Format("select top 25 Term as Label, Type, ID from SearchTerms WHERE Term like '%{0}%'", term);
var data = conn.Query(QueryString);
I get 25 rows back in the collection. Is Dapper not correctly parsing the end of the parameter #T?
Try:
term = "whateverterm";
var encodeForLike = term => term.Replace("[", "[[]").Replace("%", "[%]");
string term = "%" + encodeForLike(term) + "%";
var data = conn.Query(#"
select top 25
Term as Label,
Type,
ID
from SearchTerms
WHERE Term like #term",
new { term });
There is nothing special about like operators, you never want your params inside string literals, they will not work, instead they will be interpreted as a string.
note
The hard-coded example in your second snippet is strongly discouraged, besides being a huge problem with sql injection, it can cause dapper to leak.
caveat
Any like match that is leading with a wildcard is not SARGable, which means it is slow and will require an index scan.
Yes it does. This simple solution has worked for me everytime:
db.Query<Remitente>("SELECT *
FROM Remitentes
WHERE Nombre LIKE #n", new { n = "%" + nombre + "%" })
.ToList();
Best way to use this to add concat function in query as it save in sql injecting as well, but concat function is only support above than sql 2012
string query = "SELECT * from country WHERE Name LIKE CONCAT('%',#name,'%');"
var results = connection.query<country>(query, new {name});
The answer from Sam wasn't working for me so after some testing I came up with using the SQLite CONCAT equivalent which seems to work:
string sql = "SELECT * FROM myTable WHERE Name LIKE '%' || #NAME || '%'";
var data = IEnumerable data = conn.Query(sql, new { NAME = Name });
Just to digress on Sam's answer, here is how I created two helper methods to make searches a bit easier using the LIKE operator.
First, creating a method for generating a parameterized query, this method uses dynamic: , but creating a strongly typed generic method should be more desired in many cases where you want static typing instead of dynamic.
public static dynamic ParameterizedQuery(this IDbConnection connection, string sql, Dictionary<string, object> parametersDictionary)
{
if (string.IsNullOrEmpty(sql))
{
return null;
}
string missingParameters = string.Empty;
foreach (var item in parametersDictionary)
{
if (!sql.Contains(item.Key))
{
missingParameters += $"Missing parameter: {item.Key}";
}
}
if (!string.IsNullOrEmpty(missingParameters))
{
throw new ArgumentException($"Parameterized query failed. {missingParameters}");
}
var parameters = new DynamicParameters(parametersDictionary);
return connection.Query(sql, parameters);
}
Then adding a method to create a Like search term that will work with Dapper.
public static string Like(string searchTerm)
{
if (string.IsNullOrEmpty(searchTerm))
{
return null;
}
Func<string, string> encodeForLike = searchTerm => searchTerm.Replace("[", "[[]").Replace("%", "[%]");
return $"%{encodeForLike(searchTerm)}%";
}
Example usage:
var sql = $"select * from products where ProductName like #ProdName";
var herringsInNorthwindDb = connection.ParameterizedQuery(sql, new Dictionary<string, object> { { "#ProdName", Like("sild") } });
foreach (var herring in herringsInNorthwindDb)
{
Console.WriteLine($"{herring.ProductName}");
}
And we get our sample data from Northwind DB:
I like this approach, since we get helper extension methods to do repetitive work.
My solution simple to this problem :
parameter.Add("#nomeCliente", dfNomeCliPesquisa.Text.ToUpper());
query = "SELECT * FROM cadastrocliente WHERE upper(nome) LIKE " + "'%" + dfNomeCliPesquisa.Text.ToUpper() + "%'";

Adding a index to collection using EF 4.1 and XAML (For a highscore table)

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.