I've been looking on google but not finding anything that does the trick for me.
as you know SQL has a "where x in (1,2,3)" clause which allows you to check against multiple values.
I'm using linq but I can't seem to find a piece of syntax that does the same as the above statement.
I have a collection of category id's (List) against which I would like to check
I found something that uses the .contains method but it doesn't even build.
You have to use the Contains method on your id list:
var query = from t in db.Table
where idList.Contains(t.Id)
select t;
The syntax is below:
IEnumerable<int> categoryIds = yourListOfIds;
var categories = _dataContext.Categories.Where(c => categoryIds.Contains(c.CategoryId));
The key thing to note is that you do the contains on your list of ids - not on the object you would apply the in to if you were writing sql.
Here's an article illustrating the approach. You should indeed use the Contains method over your collection which will be translated into IN clause.
Here is my realization of WhereIn() Method, to filter IQueryable collection by a set of selected entities:
public static IQueryable<T> WhereIn<T,TProp>(this IQueryable<T> source, Expression<Func<T,TProp>> memberExpr, IEnumerable<TProp> values) where T : class
{
Expression predicate = null;
ParameterExpression param = Expression.Parameter(typeof(T), "t");
bool IsFirst = true;
MemberExpression me = (MemberExpression) memberExpr.Body;
foreach (TProp val in values)
{
ConstantExpression ce = Expression.Constant(val);
Expression comparison = Expression.Equal(me, ce);
if (IsFirst)
{
predicate = comparison;
IsFirst = false;
}
else
{
predicate = Expression.Or(predicate, comparison);
}
}
return predicate != null
? source.Where(Expression.Lambda<Func<T, bool>>(predicate, param)).AsQueryable<T>()
: source;
}
And calling of this method looks like:
IQueryable<Product> q = context.Products.ToList();
var SelectedProducts = new List<Product>
{
new Product{Id=23},
new Product{Id=56}
};
...
// Collecting set of product id's
var selectedProductsIds = SelectedProducts.Select(p => p.Id).ToList();
// Filtering products
q = q.WhereIn(c => c.Product.Id, selectedProductsIds);
Related
I have a request query using linq. The query has multiple where clause say return list of items matching name and city.
Below is the piece of code I used for multiple where clause, but it returns empty set of items.
wherefield contains list of field names like name;city
wherefieldValue contains list of field values like james;delhi
var where = FilterLinq<T>.GetWherePredicate(wherefield, wherefieldvalue).Compile();
items = items.Where(where).OrderByDescending(a => a.GetType().GetProperty(field).GetValue(a, null)).Skip
public class FilterLinq<T>
{
public static Expression<Func<T, Boolean>> GetWherePredicate(string whereFieldList, string whereFieldValues)
{
//the 'IN' parameter for expression ie T=> condition
ParameterExpression pe = Expression.Parameter(typeof(T), typeof(T).Name);
//combine them with and 1=1 Like no expression
Expression combined = null;
if (whereFieldList != null)
{
string[] field = whereFieldList.Split(';');
string[] fieldValue = whereFieldValues.Split(';');
for (int i = 0; i < field.Count(); i++)
{
//Expression for accessing Fields name property
Expression columnNameProperty = Expression.Property(pe, field[i]);
//the name constant to match
Expression columnValue = Expression.Constant(fieldValue[i]);
//the first expression: PatientantLastName = ?
Expression e1 = Expression.Equal(columnNameProperty, columnValue);
if (combined == null)
{
combined = e1;
}
else
{
combined = Expression.And(combined, e1);
}
}
}
//create and return the predicate
return Expression.Lambda<Func<T, Boolean>>(combined, new ParameterExpression[] { pe });
}
}
Your example works. Sure it works only for string properties, but i assume, that is your use case.
Perhaps it doesn't do what you want to achieve, becasue you combine your clause with and, but actually you do want to do it with Or, jus change this code line :
combined = Expression.And(combined, e1);
To
combined = Expression.Or(combined, e1);
I have the search function. and I want to select all value in my Book table which contain _searchdata but I dont know how to express at "where" with the short code instead of listing all items of Table like this:
(I just get some items for example, it contains about 100 items like Booktitle, Author, Genre... i dont want to specify it because it's so long)
public void SearchAny(string _searchdata)
{
var searchAnyInDB = from Book x in BookDB.Books
where (x.BookTitle.Contains(_searchdata)
|| x.Author.Contains(_searchdata)
|| x.Genre.Contains(_searchdata))
select x;
DataSearch.Clear();
DataSearch = new ObservableCollection<Book>(searchAnyInDB);
}
Because LINQ to Entities and LINQ to SQL both use Expression<Func<TSource, bool>> as IQueryable.Where extension method parameter, you can use reflection to create that Expression during compile type and generate all there || instead of typing them into your source code.
Would be something like:
var searchAnyInDB = from Book x in BookDB.Books
where (GetWhereExpression<Book>(_searchdata))
select x;
And GetWhereExpression<TSource> method:
static Expression<Func<TSource, bool>> GetWhereExpression<TSource>(string value)
{
var param = Expression.Parameter(typeof(TSource));
var val = Expression.Constant(value);
var expression = Expression.Equal(Expression.Constant(1), Expression.Constant(1));
foreach(var prop in typeof(TSource).GetProperties(BindingFlags.Public | BindingFlags.Instance))
{
if(prop.PropertyType == typeof(string))
{
expression = Expression.OrElse(expression,
Expression.Call(
Expression.Property(param, prop),
"Contains",
null,
val
)
);
}
}
return Expression.Lambda<Func<TSource, bool>>(expression, param);
}
You still can do better then that, ex. remembering the expression for type to prevent using reflection every time you need to execute the query with different search texts, etc. But it should give you an idea where to go.
I want to create a dynamic linq expression for sql IN clause in EF 6.0 with code first approch. Note that i am new to Expressions. What i want to achive is
select * from Courses where CourseId in (1, 2, 3, 4)
//CourseId is integer
The normal linq query looks like this. But i want to query it dynamically
string[] ids = new string[]{"1", "2", "3", "4"};
var courselist = DBEntities.Courses.Where(c => ids.Contains(SqlFunctions.StringConvert((decimal?)c.CourseId)))
There are two ways to make dynamic expression.
1) one ways is to loop through ids and make expressions
The below code will create the following expression in debug view
{f => ((StringConvert(Convert(f.CourseId)).Equals("23") Or StringConvert(Convert(f.CourseId)).Equals("2")) Or StringConvert(Convert(f.CourseId)).Equals("1"))}
Dynamic Expression is
var param = Expression.Parameters(typeof(Course), "f")
MemberExpression property = Expression.PropertyOrField(param, "CourseId");
MethodInfo mi = null;
MethodCallExpression mce = null;
if (property.Type == typeof(int))
{
var castProperty = Expression.Convert(property, typeof(double?));
var t = Expression.Parameter(typeof(SqlFunctions), "SqlFunctions");
mi = typeof(SqlFunctions).GetMethod("StringConvert", new Type[] { typeof(double?) });
mce = Expression.Call(null,mi, castProperty);
}
mi = typeof(string).GetMethod("Equals", new Type[]{ typeof(string)});
BinaryExpression bex = null;
if (values.Length <= 1)
{
return Expression.Lambda<Func<T, bool>>(Expression.Call(mce, mi, Expression.Constant(values[0]), param));
}
//var exp1 = Expression.Call(mce, mi, Expression.Constant(values[0]));
for (int i = 0; i < values.Length; i++)
{
if (bex == null)
{
bex = Expression.Or(Expression.Call(mce, mi, Expression.Constant(values[i])), Expression.Call(mce, mi, Expression.Constant(values[i + 1])));
i++;
}
else
bex = Expression.Or(bex, Expression.Call(mce, mi, Expression.Constant(values[i])));
}//End of for loop
return Expression.Lambda<Func<T, bool>>(bex, param);
2) The 2nd way that i tried (debug view)
{f => val.Contains("23")} //val is parameter of values above
The dynamic expression for above that i tried is
var param = Expression.Parameters(typeof(Course), "f")
MemberExpression property = Expression.PropertyOrField(param, "CourseId");
var micontain = typeof(Enumerable).GetMethods().Where(m => m.Name == "Contains" && m.GetParameters().Length == 2).Single().MakeGenericMethod(typeof(string));
var mc = Expression.Call(micontain, Expression.Parameter(values.GetType(), "val"), Expression.Constant("2"));//NOTE: I haven't use CourseId for now as i am getting conversion error
return Expression.Lambda<Func<T, bool>>(mc, param);
I get the following errors
LINQ to Entities does not recognize the method 'System.String StringConvert(System.Nullable`1[System.Double])' method, and this
method cannot be translated into a store expression when i use the
first methodology. I know i can't use ToString with EF thats why I used SqlFunctions but it is not working for me.
The parameter 'val' was not bound in the specified LINQ to Entities query expression using 2nd methodology
I am trying this from last 4 days. I googled it but didn't find any suitable solution. Please help me.
After a lot of struggle I found solution to my question.
I want to achieve this sql query
select * from Courses where CourseId in (1, 2, 3, 4)
Using Linq to Entities, but I want to pass in(1,2,3,4) list dynamically to linq query. I created an Extension class for that purpose.
public static class LinqExtensions
{
public static Expression<Func<T, bool>> False<T>() { return f => false; }
public static Expression<Func<T, bool>> In<T, TValue>(this Expression<Func<T, bool>> predicate,string propertyName, List<TValue> values)
{
var param = predicate.Parameters.Single();
MemberExpression property = Expression.PropertyOrField(param, propertyName);
var micontain = typeof(List<TValue>).GetMethod("Contains");
var mc = Expression.Call(Expression.Constant(values), micontain, property);
return Expression.Lambda<Func<T, bool>>(mc, param);
}
}
Use of LinqExtensions
var pred = LinqExtensions.False<Course>(); //You can chain In function like LinqExtensions.False<Course>().In<Course, int>("CourseId", inList);
var inList= new List<int>(){1, 2, 3}; //Keep in mind the list must be of same type of the Property that will be compared with. In my case CourseId is integer so the in List have integer values
pred =pred.In<Course, int>("CourseId", inList); //TValue is int. As CourseId is of type int.
var data = MyEntities.Courses.Where(pred);
I hope this might be beneficial for some one
have you seen the type of
var courselist = DBEntities.Courses.Where(c => ids.Contains(c.CourseId)))
above statement would not return actual list of courses. The query is not executed yet. It just returns IQuereable. The query is executed when you actually call .ToList() method on it
so, your solution is..
Create array of IDs using for loop and then simply run the below query
var courselist = DBEntities.Courses.Where(c => ids.Contains(c.CourseId))).ToList()
I have created a dynamic search screen in ASP.NET MVC. I retrieved the field names from the entity through reflection so that I could allow the user to choose which fields they wanted to search on instead of displaying all fields in the view.
When the search result is Posted back to the controller, I receive a FormCollection containing the FieldName and the Value. I don't know how many fields are being searched on, and the FormCollection only contains fields that were chosen by the user.
I want to be able to now take that field name and apply that to my LINQ statement when I query the database for example:
public List<People> SearchPeople(Dictionary<string, string> fieldValueDictionary)
{
List<People> searchResults = new List<People>();
foreach (string key in fieldValueDictionary.Keys)
{
searchResults.Add(entities.People.Where(p => p.<use the key string as the fieldName> == fieldValueDictionary[key]));
}
return searchResults;
}
Where I have "use the key string as the fieldName" it would be like p => p.FirstName == fieldValueDictionary[key] where key = "FirstName". I've tried and failed to use Lambda Expression Trees, and have had a little success with Dynamic LINQ. The only other alternative is to do something like:
public List<People> SearchPeople(Dictionary<string, string> fieldValueDictionary)
{
IQueryable<People> results = entities.People;
foreach (string key in fieldValueDictionary.Keys)
{
switch (k)
{
case "FirstName": results = results.Where(entities.People.Where(p => p.FirstName == k);
case "LastName": results = results.Where(entities.People.Where(p => p.LastName == k);
// Repeat for all 26 fields in table
}
}
return results.ToList<People>();
}
UPDATE: I've done research into Lambda Expression Trees through the following posts:
dynamically create lambdas expressions + linq + OrderByDescending
Parameter problem with Expression.Lambda()
LINQ: Passing lambda expression as parameter to be executed and returned by method
I've gotten as far as getting a lambda to output the following: "p => p.FirstName", but I can't get this to work in a where. Any Suggestions? My code is below:
MemberInfo member = typeof(People).GetProperty("FirstName");
ParameterExpression cParam = Expression.Parameter(typeof(People), "p");
Expression body = Expression.MakeMemberAccess(cParam, member);
var lambda = Expression.Lambda(body, cParam);
After a lot more trial and error and searching I accidentally found another SO post that covers the same issue:
InvalidOperationException: No method 'Where' on type 'System.Linq.Queryable' is compatible with the supplied arguments
Here is my modified code that works:
IQueryable query = entities.People;
Type[] exprArgTypes = { query.ElementType };
string propToWhere = "FirstName";
ParameterExpression p = Expression.Parameter(typeof(People), "p");
MemberExpression member = Expression.PropertyOrField(p, propToWhere);
LambdaExpression lambda = Expression.Lambda<Func<People, bool>>(Expression.Equal(member, Expression.Constant("Scott")), p);
MethodCallExpression methodCall = Expression.Call(typeof(Queryable), "Where", exprArgTypes, query.Expression, lambda);
IQueryable q = query.Provider.CreateQuery(methodCall);
With some hopefully pretty easy modifications, I should be able to get this to work with any type.
Thanks again for your answers Ani & John Bowen
Have you tried getting the value from PropertyInfo?
entities.People.Where(p => (p.GetType().GetProperty(key).GetValue(p, null) as string) == fieldValueDictionary[key])
public List<People> SearchPeople(Dictionary<string, string> fieldValueDictionary)
{
return !fieldValueDictionary.Any()
? entities.People
: entities.People.Where(p => fieldValueDictionary.All(kvp => PropertyStringEquals(p, kvp.Key, kvp.Value)))
.ToList();
}
private bool PropertyStringEquals(object obj, string propertyName, string comparison)
{
var val = obj.GetType().GetProperty(propertyName).GetValue(obj, null);
return val == null ? comparison == null : val.ToString() == comparison; ;
}
How do I write a dynamic query for Linq, if I have say Customer class which holds the fields:
string name
string address
int phoneno
I have to query based on information given similar to
query = string.Empty;
if(!string.IsNullorEmpty(name))
{
query += "#name = name";
}
if(!string.IsNullorEmpty(address))
{
query += "#address = address";
}
if(!string.IsNullorEmpty(phoneno))
{
query += "#phoneno = phoneno";
}
var result = from condition in customer
where(query)
select condition;
Edit #1:
the items are changeable at run time like
private Customer[] GetCustomers(Dictionary<string,string> attributes)
{
here the attribute may be, name alone, or name and address, or name address and phoneno
foreach(string field in attributes.key)
{
query += field == attributes[key];
}
Customers[] =ExecuteQuery(query);
}
Is this kind of query supported by LINQ?
Edit #2:
Hi Mouk,
As I am new to C#, I am still struggling, this is not working for me.
var query = _ConfigFile.ConnectionMasterSection;
for(int i = 0; i < filter.count; i++)
{
query = result.Where(p => typeof(ConnectionMaster).GetProperty(filter[i].Attribute).Name == filter[i].Value);
}
This yeilds Empty, where as i used this
var query = _ConfigFile.ConnectionMasterSection;
//Hard coded
res.Where(q => q.category == filter[0].Value);
And it worked as I expected.
Hi Bryan Watts,
I tried your code also and I getting this error: "Lambda Parameter not in scope".
for(int i = 0; i < filter.count; i++)
{
Field item = filter[i];
MemberExpression param = Expression.MakeMemberAccess(Expression.Parameter(typeof(Connection), "p"), typeof(Connection).GetProperty(item.Attribute));
MemberExpression constant = Expression.MakeMemberAccess(Expression.Constant(item), typeof(Field).GetProperty("Value"));
}
try
{
var myquery = Queryable.Where(coll, Expression.Lambda<Func<Connection, bool>>(
Expression.Equal(param, constant), Expression.Parameter(typeof(Connection),"p")));
}
What is the mistake here?
Check out this http://www.albahari.com/nutshell/predicatebuilder.aspx, it allows for strongly typed predicate building, it can be really nice. If you want actually dynamic string built predicates than you can use the LINQ Dynamic Query Library provided by ScottGu.
Both will accomplish what you want although I would recommend the first option before the second.
Allowing you to do:
var predicate = PredicateBuilder.True<MyLinqType>();
if(!string.IsNullOrEmpty(name))
predicate = predicate.And(p => p.name == name);
...
var myResults = Context.MyLinTypeQueryTable.Where(predicate);
And more.
Here you go:
var result = from customer in Customers
where string.IsNullOrEmpty(phoneNo) || customer.PhoneNo == phoneNo
where string.IsNullOrEmpty(address) || customer.Address == address
select customer;
If you're concerned that this generate the optimal SQL query underneath, as always you should attach a SQL Query Analyzer and check. But I believe the expression parser in Linq To Sql will collapse down the where clauses as appropriate based on the value of the arguments.
You can use the fluent interface and add a new Where clause fpr each condition. Something like:
var result = from cus in customers select cus;
if(!string.IsNullOrEmpty(name))
result= result.Where(p => p.Name == name);
EDIT upon hte comment:
if you are querying over a collection in memory, you could retrieve the properties using reflection.
private Customer[] GetCustomers(Dictionary<string,string> attributes)
{
var result = from cus in customers select cus;
foreach(string key in attributes.Keys)
result= result.Where(p => GetProperty(p, key )== attributes[key]);
return result.ToList();
}
Supposing GetProperty retrieve the property by reflection.
Using Linq2Sql this method will result in retrieving all record an then iterating over them using reflection.
I've had good experience with Dynamic LINQ.
I used it for a rich HTML table that could be filtered and sorted server side. The server receives a request containing a request parameter where the key is the name of the property (for example 'Lastname') and the value is the value that the property needs to be sorted on (for example 'Smith'). Using that information I built a query string that I passed to the Dynamic LINQ's Where method.
Roughly, you could think of something like the following:
public static IQueryable<T> Filter<T>(this IQueryable<T> query, Dictionary<string, string> dictionary)
{
Type t = typeof(T);
StringBuilder sb = new StringBuilder();
PropertyInfo[] properties = t.GetProperties();
foreach(string key in dictionary.Keys)
{
PropertyInfo property = properties.Where(p => p.Name == key).SingleOrDefault();
if(property != null)
{
if (sb.Length > 0) sb.Append(" && ");
string value = dictionary[key];
sb.Append(string.Format(#"{0}.ToString().Contains(""{1}"")", key, value));
}
}
if (sb.Length > 0)
return query.Where(sb.ToString());
else
return query;
}
The code is out of the top of my head and thus untested.
Of course, this is the most basic version: it does a simple string comparison. If you want to have numerical comparison (meaning you want for example the User where UserID is exactly 100, not where the UserID.ToString().Contains("100")), or query nested Properties (Customer.Company.CompanyAddress for example), or query Collections this gets more complicated. You should also think about security: while Dynamic LINQ is not vulnerable to SQL injection, you shouldn't let it blindly parse all user input.
It sounds like you need to dynamically compose queries.
See my answer to this question.
It explains how queries against an IQueryable<T> are composed by the compiler, and what you can do to add dynamic elements.
Edit
Here is an example of how you would dynamically build a set of Where conditions on top of an IQueryable<Customer>:
// This method ANDs equality expressions for each property, like so:
//
// customers.Where(c => c.Property1 == value1 && c.Property2 == value2 && ...);
private IQueryable<Customer> FilterQuery(IQueryable<Customer> customers, IDictionary<string, string> filter)
{
var parameter = Expression.Parameter(typeof(Customer), "c");
Expression filterExpression = null;
foreach(var filterItem in filter)
{
var property = typeof(Customer).GetProperty(filterItem.Key);
var propertyAccess = Expression.MakeMemberAccess(parameter, property);
var equality = Expression.Equal(propertyAccess, Expression.Constant(filterItem.Value));
if(filterExpression == null)
{
filterExpression = equality;
}
else
{
filterExpression = Expression.And(filterExpression, equality);
}
}
if(filterExpression != null)
{
var whereBody = Expression.Lambda<Func<Customer, bool>>(filterExpression, parameter);
customers = customers.Where(whereBody);
}
return customers;
}