Hi I am looking for best method for writing Dynamic LINQ query.
I have a function like
public IQueryable<Student> FindByAllStudents(int? id, string Name, int? CourseID, bool? IsActive) // like this way, all field values are passed
{
// code for compairision
return db.Student;
}
we can also write db.Students.where(predicate)
or
a query like
var students = from s in db.students where s.Name.Contains(Name)
s.ID.Equals(id)
//and so on....
So will this method works if i don't pass ID (i.e. Null)?
is proper way for all the datatypes?
The point is function can have all null values as a parameter for equivalence of select * from statement.
can any one help me to build best query with sample code?
Okay, it's not entirely clear what you want, but if you're trying to only add where clauses for the parameters which are non-null, you could do:
public IQueryable<Student> FindByAllStudents
(int? id, string name, int? courseID, bool? isActive)
{
IQueryable<Student> query = db.Student;
if (id != null)
{
query = query.Where(student => student.ID == id.Value);
}
if (name != null)
{
query = query.Where(student => student.Name.Contains(name));
}
if (courseID != null)
{
query = query.Where(student => student.CourseID == courseID.Value);
}
if (isActive != null)
{
query = query.Where(student => student.IsActive == isActive.Value);
}
return query;
}
I haven't tried that, and it's possible that LINQ to SQL would get confused by the code to find the value of the nullable value types. You may need to write code like this:
if (courseID != null)
{
int queryCourseID = courseID.Value;
query = query.Where(student => student.CourseID == queryCourseID);
}
It's worth trying the simpler form first though :)
Of course, all this gets a bit irritating. A helpful extension method could make life more concise:
public static IQueryable<TSource> OptionalWhere<TSource, TParameter>
(IQueryable<TSource> source,
TParameter? parameter,
Func<TParameter, Expression<Func<TSource,bool>>> whereClause)
where TParameter : struct
{
IQueryable<TSource> ret = source;
if (parameter != null)
{
ret = ret.Where(whereClause(parameter.Value));
}
return ret;
}
You'd then use it like this:
public IQueryable<Student> FindByAllStudents
(int? id, string name, int? courseID, bool? isActive)
{
IQueryable<Student> query = db.Student
.OptionalWhere(id, x => (student => student.ID == x))
.OptionalWhere(courseID, x => (student => student.CourseID == x))
.OptionalWhere(isActive, x => (student => student.IsActive == x));
if (name != null)
{
query = query.Where(student => student.Name.Contains(name));
}
return query;
}
Using a higher order function like this could get confusing if you're not really comfortable with it though, so if you're not doing very many queries like this you might want to stick with the longer but simpler code.
Related
need small help about returning values based on arguments.
Setup of mocking contains expressions like
mockingObject
.Setup(_=>_.Select(It.IsAny<Expression<Func<Entity, bool>>>(),
It.IsAny<Func<IQueryable<Entity>, IOrderedQueryable<Entity>>>(),
It.IsAny<List<Expression<Func<Entity, object>>>>(), It.IsAny<int?>(), It.IsAny<int?>())))
.ReturnsAsync((Expression<Func<Entity,bool>>,Func<IQueryable<Entity>, IOrderedQueryable<Entity>>,List<Expression<Func<Entity,object>>>,int, int,EntityList());
But I'm getting error that Expression<Func<Entity,bool>> is a type which is not valid give context.
How should I manage Returns?
Need to mock:
public async Task<Result> UpdateNetworkStatus(string id, NetworkStatus status)
{
var network = _unitOfWork.NetworkRepository.SelectListAsync(x => x.Id == id).Result.FirstOrDefault();
if (network == null)
throw new Exception(nameof(network));
network.Status = status;
_unitOfWork.NetworkRepository.Update(network);
var saved = await _unitOfWork.Commit();
if (!saved)
return Result.Failure(new List<string>
{
"Failed to save"
});
return Result.Success();
}
Here I need to mock all possible scenarios.
Here is the example how I had manage to pass args to returns
unitOfWorkMock.Setup(_ => _.EntityRepository.SelectListAsync(It.IsAny<Expression<Func<Entity, bool>>>(),
It.IsAny<Func<IQueryable<Entity>, IOrderedQueryable<Entity>>>(),
It.IsAny<List<Expression<Func<Entity, object>>>>(), It.IsAny<int?>(), It.IsAny<int?>()))
.ReturnsAsync((Expression<Func<Entity, bool>> filter, Func<IQueryable<Entity>, IOrderedQueryable<Entity>> orderBy, List<Expression<Func<Entity, object>>> includes, int? page, int? pageSize) =>
{
if (filter == null)
return Entities();
return Entities().AsQueryable().Where(filter).ToList();
});
I have a Category entity which has a Nullable ParentId field. When the method below is executing and the categoryId is null, the result seems null however there are categories which has null ParentId value.
What is the problem in here, what am I missing?
public IEnumerable<ICategory> GetSubCategories(long? categoryId)
{
var subCategories = this.Repository.Categories.Where(c => c.ParentId == categoryId)
.ToList().Cast<ICategory>();
return subCategories;
}
By the way, when I change the condition to (c.ParentId == null), result seems normal.
Other way:
Where object.Equals(c.ParentId, categoryId)
or
Where (categoryId == null ? c.ParentId == null : c.ParentId == categoryId)
The first thing to do is to put on logging, to see what TSQL was generated; for example:
ctx.Log = Console.Out;
LINQ-to-SQL seems to treat nulls a little inconsistently (depending on literal vs value):
using(var ctx = new DataClasses2DataContext())
{
ctx.Log = Console.Out;
int? mgr = (int?)null; // redundant int? for comparison...
// 23 rows:
var bosses1 = ctx.Employees.Where(x => x.ReportsTo == (int?)null).ToList();
// 0 rows:
var bosses2 = ctx.Employees.Where(x => x.ReportsTo == mgr).ToList();
}
So all I can suggest is use the top form with nulls!
i.e.
Expression<Func<Category,bool>> predicate;
if(categoryId == null) {
predicate = c=>c.ParentId == null;
} else {
predicate = c=>c.ParentId == categoryId;
}
var subCategories = this.Repository.Categories
.Where(predicate).ToList().Cast<ICategory>();
Update - I got it working "properly" using a custom Expression:
static void Main()
{
ShowEmps(29); // 4 rows
ShowEmps(null); // 23 rows
}
static void ShowEmps(int? manager)
{
using (var ctx = new DataClasses2DataContext())
{
ctx.Log = Console.Out;
var emps = ctx.Employees.Where(x => x.ReportsTo, manager).ToList();
Console.WriteLine(emps.Count);
}
}
static IQueryable<T> Where<T, TValue>(
this IQueryable<T> source,
Expression<Func<T, TValue?>> selector,
TValue? value) where TValue : struct
{
var param = Expression.Parameter(typeof (T), "x");
var member = Expression.Invoke(selector, param);
var body = Expression.Equal(
member, Expression.Constant(value, typeof (TValue?)));
var lambda = Expression.Lambda<Func<T,bool>>(body, param);
return source.Where(lambda);
}
My guess is that it's due to a rather common attribute of DBMS's - Just because two things are both null does not mean they are equal.
To elaborate a bit, try executing these two queries:
SELECT * FROM TABLE WHERE field = NULL
SELECT * FROM TABLE WHERE field IS NULL
The reason for the "IS NULL" construct is that in the DBMS world, NULL != NULL since the meaning of NULL is that the value is undefined. Since NULL means undefined, you can't say that two null values are equal, since by definition you don't know what they are.
When you explicitly check for "field == NULL", LINQ probably converts that to "field IS NULL". But when you use a variable, I'm guessing that LINQ doesn't automatically do that conversion.
Here's an MSDN forum post with more info about this issue.
Looks like a good "cheat" is to change your lambda to look like this:
c => c.ParentId.Equals(categoryId)
You need to use operator Equals:
var subCategories = this.Repository.Categories.Where(c => c.ParentId.Equals(categoryId))
.ToList().Cast<ICategory>();
Equals fot nullable types returns true if:
The HasValue property is false, and the other parameter is null. That is, two null values are equal by definition.
The HasValue property is true, and the value returned by the Value property is equal to the other parameter.
and returns false if:
The HasValue property for the current Nullable structure is true, and the other parameter is null.
The HasValue property for the current Nullable structure is false, and the other parameter is not null.
The HasValue property for the current Nullable structure is true, and the value returned by the Value property is not equal to the other parameter.
More info here Nullable<.T>.Equals Method
Or you can simply use this. It will also translate to a nicer sql query
Where((!categoryId.hasValue && !c.ParentId.HasValue) || c.ParentId == categoryId)
What about something simpler like this?
public IEnumerable<ICategory> GetSubCategories(long? categoryId)
{
var subCategories = this.Repository.Categories.Where(c => (!categoryId.HasValue && c.ParentId == null) || c.ParentId == categoryId)
.ToList().Cast<ICategory>();
return subCategories;
}
Linq to Entities supports Null Coelescing (??) so just convert the null on the fly to a default value.
Where(c => c.ParentId == categoryId ?? 0)
I am using oracleDB and i have view like below which contains employees and his managers.
empNo
FirstName
LastName
Manager
I need to select a person and all of his staff. IE
Person1 is Manager
-- Person1_1
----Person1_1_1
----Person1_1_2
-- Person1_1
When i login with the user of Person1, I need to get all of the persons above.
Here is my LINQ but it is too slow.. What is the efficient way to get the data ?
List<decimal> OrgPerson2 = new List<decimal>();
public List<decimal> getOrgPerson(decimal empNo)
{
List<decimal> OrgPerson = new List<decimal>();
OrgPerson.AddRange(db.CRM_PERSON_TITLE_V.Where(c => c.MANAGER == empNo).Select(c => (decimal)c.PERSONID).ToList());
var subPerson = db.CRM_PERSON_TITLE_V.ToList();
foreach (var item in OrgPerson)
{
OrgPerson2.Add(item);
var subPerson2 = subPerson.Where(c => c.MANAGER == item).Select(c => (decimal)c.PERSONID).ToList();
if (subPerson2 != null)
{
if (subPerson2.Count > 0)
{
getOrgPerson(item);
}
}
}
return OrgPerson2.Distinct().ToList();
}
Decided to try out your solution and as I suspected it threw a StackOverflowException for me. Recursive methods are pretty bad if you are not careful.
Here's my solution with a stack. The code is self-explanatory.
List<decimal> GetOrgPerson(decimal id)
{
Stack<Person> iter = new Stack<Person>();
List<decimal> result = new List<decimal>();
iter.Push(db.People.FirstOrDefault(p => p.ID == id));
while (iter.Count() > 0)
{
Person current = iter.Pop();
var subordinates = db.People.Where(p => p.ManagerID == current.ID);
foreach (var s in subordinates)
{
if (result.Contains(s.ID))
continue;
iter.Push(s);
result.Add(s.ID);
}
}
return result;
}
In my test-case People inherits IEnumerable interface.
Your query is just getting all the staff under a manager recursively, it can be greatly simplified:
public IEmunerable<decimal> getOrgPerson(decimal empNo)
{
foreach (var subEmpNo in db.CRM_PERSON_TITLE_V.Where(c => c.MANAGER == empNo).Select(c => (decimal)c.PERSONID))
{
yield return subEmpNo;
foreach (var subSubEmpNo in getOrgPerson(subEmpNo))
yield return subSubEmpNo;
}
}
You should not need Distinct() since each employee has only one manager.
Also, I assume you don't need a List<decimal> which you can add/remove items. Otherwise, you may need something like OrgPerson2 = getOrgPerson(empNo).ToList()
// Hi everyone
i do this call in Action :
[HttpGet]
public virtual ActionResult JsonGetProvinces(int countryId)
{
//WebSiteContext WbContext = new WebSiteContext();
//UnitOfWork UnitofWork = new UnitOfWork(WbContext);
var provinces =
(
from province in unitofWork.ProvinceRepository.All
where province.CountryId == countryId
select new
{
Id = province.Id,
Name = province.GetType().GetProperty("Name_" + CultureManager.GetCurrentCultureShortName()).GetValue(province)
}
).ToList();
return Json(provinces, JsonRequestBehavior.AllowGet);
}
something is wrong with my query :
var provinces =
(
from province in unitofWork.ProvinceRepository.All
where province.CountryId == countryId
select new
{
Id = province.Id,
Name = province.GetType().GetProperty("Name_" + CultureManager.GetCurrentCultureShortName()).GetValue(province)
}
).ToList();
Particulary,
Name = province.GetType().GetProperty("Name_" + CultureManager.GetCurrentCultureShortName()).GetValue(province)
In BDD, there is Name_fr, Name_en columns
and i'm trying to take one dynamically... Is it possible ?
Of course, i can take both and choose dynamically the column in View but i would to know how do...
Thank you for your help
The short answer is you need to change your code a bit and using expression tree inside. Look at this question
EF can not translate function calls to SQL. Using expression trees can be comlicated see this question
Here is a sample with expression trees. The GetQuery2 is the same as GetQuery but with expression tree and a propertyname parameter.
public static IQueryable<Foo> GetQuery(BlogContext context)
{
var query = from x in context.BlogEntries
select new Foo
{
NameX = x.Name
};
return query;
}
public static IQueryable<Foo> GetQuery2(BlogContext context, string propertyName)
{
ConstructorInfo ci = typeof(Foo).GetConstructor(new Type[0]);
MethodInfo miFooGetName = typeof(Foo).GetMethod("set_NameX");
MethodInfo miBlogEntry = typeof(BlogEntry).GetMethod("get_" + propertyName);
ParameterExpression param = Expression.Parameter(typeof(BlogEntry), "x");
IQueryable<Foo> result = Queryable.Select<BlogEntry, Foo>(
context.BlogEntries,
Expression.Lambda<Func<BlogEntry, Foo>>(
Expression.MemberInit(
Expression.New(ci, new Expression[0]),
new MemberBinding[]{
Expression.Bind(miFooGetName,
Expression.Property(param,
miBlogEntry))}
),
param
)
);
return result;
}
It is easier the fetch all all language strings and write an additional Property Name that does the magic.
I am using the following code to first check if a string is located somewhere within a column in my database. If it is, I am then needing to check if a few additional criteria are met by looking at different parts of the database (can be seen in the code below). I am not sure if this is an efficient method for doing this or if there is a much simpler way:
(from my Controller)
[HttpPost]
public ActionResult Index(FormCollection sampleKey)
{
string code = sampleKey["sampleCode"];
ViewBag.code = code;
// Need to check if this code is active
var order = db.Orders.SingleOrDefault(
o => o.OrderCode == code
&& o.Active == true);
if (order == null)
{
//Invalid
}
else
{
var orderIdent = db.OrderDetails.SingleOrDefault(
p => p.OrderDetailId == order.OrderId);
var barIdent = db.Drink.SingleOrDefault(
q => q.EstablishmentsID == orderIdent.DrinksId);
var barName = db.Establishment.SingleOrDefault(
r => r.EstablishmentsId == barIdent.EstablishmentsID);
ViewBag.barId = barName.name;
ViewBag.sample = order.Email;
var custProfile = CustomProfile.GetUserProfile();
if (custProfile.OwnedBar != barName.name)
{
//Not a match
}
else
{
//Match
}
}
return View();
}
Is this something to worry about? Is there a more efficient way of performing the actions that I am currently performing? Should I change the first table that is referenced to include data from the table I ultimately compare it to to avoid what seems to be an inefficient way of comparing information from different tables?
You should check the SQL query that gets generated. You can do that by e.g. outputting the queries to the console, which is done by setting db.Log = Console.Out;. There should be a similar method to output to the web page in your case. The lazy nature of LINQ makes things difficult to predict.
Other than that, you could make your life much easier if you create foreign key relationships between your tables, i.e. OrderDetails has Orders.OrderId as a FK. This will allow Entity Framework to generate navigational properties for your database. With them your code would look like this:
[HttpPost]
public ActionResult Index(FormCollection sampleKey)
{
string code = sampleKey["sampleCode"];
var detail = db.Orders.Where(o => o.OrderCode == code && o.Active == true)
.Select(o => new {
OrderCode = o.OrderCode,
BarId = o.Drink.Establishment.Select(n => n.name),
Sample = o.Email
})
.SingleOrDefault();
if (detail != null)
{
ViewBag.code = detail.OrderCode;
ViewBag.barId = detail.BarId;
ViewBag.sample = detail.Sample;
var custProfile = CustomProfile.GetUserProfile();
if (custProfile.OwnedBar == detail.BarId)
{
//Match
}
else
{
//Not a match
}
}
else
{
//Invalid
}
return View();
}