I have a database that has a user search screen that is "dynamic" in that I can add additional search criteria on the fly based on what columns are available in the particular view the search is based on and it will allow the user to use them immediately. Previously I had been using nettiers for this database, but now I am programming a new application against it using RIA and EntFramework 4 and LINQ.
I currently have 2 tables that are used for this, one that fills the combobox with the available search string patterns:
LastName
LastName, FirstName
Phone
etc....
then I have an other table that splits those criteria out and is used in my nettiers algorithms. It works well, but I want to use LINQ..and it doesnt fit this model very well. Besides I think I can pare it down to just one table with linq...
using a format similar to this or something very close...
ID Criteria WhereClause
1 LastName 'Lastname Like '%{0}%'
now I know this wont fit specifically into a linq query..but I am trying to use a univeral syntax for clarity here...
the real where clause would look something like this: a=>a.LastName.Contains("{0}")
My first question is: Is that even possible to do? Feed a lambda in to a string and use it in a Linq Query?
My second question is: at one point when I was researching this before I found a linq syntax that had a prefix like it.LastName{0}
and I appear to have tried using it because vestiges of it are still in my test databases...but I dont know recall where I read about it.
Is anyone doing this? I have done some searches and found similar occurances but they mostly have static fields that are optional, not exactly the way I am doing it...
As for your first question, you can do this using Dynamic Linq as described by Scott Gu here
var query = Northwind.Products.Where("Lastname LIKE "test%");
I'm not sure how detailed your dynamic query needs to be, but when I need to do dynamic queries, I create a class to represent filter values. Then I pass that class to a search method on my repository. If the value for a field is null then the query ignores it. If it has a value it adds the appropriate filter.
public class CustomerSearchCriteria{
public string LastName { get; set; }
public string FirstName { get; set; }
public string PhoneName { get; set; }
}
public IEnumberable<Customer> Search(CustomerSearchCriteria criteria){
var q = db.Customers();
if(criteria.FirstName != null){
q = q.Where(c=>c.FirstName.Contains(criteria.FirstName));
}
if(criteria.LastName!= null){
q = q.Where(c=>c.LastName.Contains(criteria.LastName));
}
if(criteria.Phone!= null){
q = q.Where(c=>c.Phone.Contains(criteria.Phone));
}
return q.AsEnumerable();
}
Related
Let's say I have this kind of model:
public class MyModel
{
public long ID { get; set; }
public long ParentModelID { get; set; }
public long ReferenceID1 { get; set; }
public long ReferenceID2 { get; set; }
}
There are more attributes, but for examples sake, it is just this. There are around 5000 - 10000 rows of this model. Currently storing it in a Redis Set.
Is there an efficient way in REDIS to query only a subset of the whole Data Set? For example, in LINQ I can do:
allModels.Where(m => m.ParentModelID == my_id);
or
allModels.Where(m => m.ReferenceID1 == my_referenceid);
Basically, being able to search through the dataset without returning the whole dataset and performing the LINQ queries against that. Because querying and returning 10,000 rows to get only 100 is not efficient?
You can use an OHM (Object-Hash Mapper, like ORM) in your favorite language to achieve the LINQ-like behavior. There are quite a few listed under the "Higher level libraries and tools" section of the [Redis Clients page](https://redis.io/clients.
Alternatively, you can implement it yourself using the patterns described at https://redis.io/topics/indexes.
You can't use something like LINQ in Redis out of the box. Redis is just a key-value store, so it doesn't have the same principles or luxuries as a relational database. It doesn't have queries or relations, so something like LINQ just doesn't translate at all.
As a workaround, you could segment your data using different keys. Each key could reference a set that stores values with a specific range of reference Ids. That way you wouldn't need to retrieve all 10,000 items.
I would also recommend looking at hashes, this might be more appropriate than a set depending on your use case as they're better at storing complex data objects.
Question is in the title. Can we programmatically change the database table which an object in the Model class, like one below, refers to and continue to operate on the new table?
public class Word
{
public int ID { get; set; }
public string Text { get; set; }
}
This originally refers to "Words" table automatically in EntityFramework, is there a way to change it before/during runtime? If so, how?
EDIT:
I get all the string used in Views in the project from the database table, "Words", by their ID's. Now, what I want is, a user enters a new language to system, and a new table will be created, for example WordsEnglish. From then, the Word object will refer to WordEnglish, if user selects English as language.
It would be desirable with a use case to better understand what you are trying to accomplish, but here goes...
In the DbContext.OnModelCreating method you can configure the model, e.g.
// Removes pluralization convention for all tables.
modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
or
// Specific table name for Word Entity.
modelBuilder.Entity<Word>().ToTable("TableContainingWords");
If you are changing your model, Code First Migrations might be what you need.
I havent found a way to truly dynamically extend an EF model at runtime. Given what goes on in DB context inherited class, the use of generated views for performance and a model class approach, avoiding recompilation seems hard. I have generated code, compiled and access this using assembly discovery approaches. But this is all unsatisfactory from my viewpoint , so i have stopped investigating this path. Very clunky outcome.
Ironically the topic you provide as a use case for such a problem, is one that doesnt need dynamic EF in my view.
I have exactly the same use case, language specific look for messages/labels etc Ie a language specific textpool.
Why not add language to the class/table.
Use a table or Enum for supported languages.
Use Language in the Textpool table/s
Use a different model class for presentation. (view model).
So you can present it the way like .
public class Word
{
Guid ID {get;set;} // logical key is WordID + Language
public int WordID { get; set; } // implement with new id or 2 field key
public Language Language {get;set;} // see cultureInfo for more details
public bool IsMaster {get;set;}
public string Text { get; set; } // consider renaming due to reserved word implications
}
public class language
{
int ID,
String Lang
}
}
The ViewModel looks like this:
public W { get; set; }
public WC WC { get; set; }
public List<TC> TCs { get; set; }
WC has a correlated group of TC. Their relation is mapped by TC containing the foreign key WCId.
In the view, I have a form. In the form, there are input fields for WC. Then, there is a group of TC depending on a count with a max of 4. Each TC has a related T in that TC has a foreign key TCId. I am trying to make sure that when the form is posted TC has the correlating TId. The TId is held in a list of T in W (i.e. #Model.W.T.ElementAt(someindex).TId).
How can I levarage a lambda expression to use the helpers to generate this relation in the view so it can be consumed in a httppost action by the correlating controller?
Here is what I am doing right now:
<input type="hidden" value="#(Model.W.T.ElementAt(i).TId)"
name="TCs[#(i)].TId"
id="TCs_#(i)__TId" data-val="true"/>
What I would like to do is use the #Html.HiddenFor helper but cannot seem to get it to work so I just used the slightly dynamic yet still hardcoded approach above. Note: this works, however, I would like it to be cleaner.
What you're doing right now is -as far as I know - the only way to do it. I don't know of a way for a simpler #Htm.HiddenFor(...) version. I've been dealing with similar issues too. Nevertheless, if you think that you could reuse the pattern above you can still create your own Display/Editor template or other more abstract ways. Of course they'll be more verbose and complex than your "ugly" but straight forward approach.
I made this into a helper, and have decided to share it in case anyone else comes across this issue.
Helper:
public static MvcHtmlString CustomHiddenFor(
this HtmlHelper html, object ListValue,
string ListName, int ListIndex, string ListItem)
{
return MvcHtmlString.Create(
string.Format("<input type=\"hidden\" value=\"{0}\" name=\"{1}[{2}].{3}\" id=\"{1}_{2}__{3}\" data-val=\"true\"/>",
ListValue.ToString(),
ListName,
ListIndex,
ListItem
));
}
Use (note that this is done from a loop where i is the iterator, any value will due in the first spot):
#Html.CustomHiddenFor(Model.W.T.ElementAt(i).TId, "TCs", i, "TId")
We are building dynamic search expressions using the Dynamic Linq library. We have run into an issue with how to construct a lamba expression using the dynamic linq library for navigation properties that have a one to many relationship.
We have the following that we are using with a contains statement-
Person.Names.Select(FamilyName).FirstOrDefault()
It works but there are two problems.
It of course only selects the FirstOrDefault() name. We want it to use all the names for each person.
If there are no names for a person the Select throws an exception.
It is not that difficult with a regular query because we can do two from statements, but the lambda expression is more challenging.
Any recommendations would be appreciated.
EDIT-
Additional code information...a non dynamic linq expression would look something like this.
var results = persons.Where(p => p.Names.Select(n => n.FamilyName).FirstOrDefault().Contains("Smith")).ToList();
and the class looks like the following-
public class Person
{
public bool IsActive { get; set;}
public virtual ICollection<Name> Names {get; set;}
}
public class Name
{
public string GivenName { get; set; }
public string FamilyName { get; set; }
public virtual Person Person { get; set;}
}
We hashed it out and made it, but it was quite challenging. Below are the various methods on how we progressed to the final result. Now we just have to rethink how our SearchExpression class is built...but that is another story.
1. Equivalent Query Syntax
var results = from person in persons
from name in person.names
where name.FamilyName.Contains("Smith")
select person;
2. Equivalent Lambda Syntax
var results = persons.SelectMany(person => person.Names)
.Where(name => name.FamilyName.Contains("Smith"))
.Select(personName => personName.Person);
3. Equivalent Lambda Syntax with Dynamic Linq
var results = persons.AsQueryable().SelectMany("Names")
.Where("FamilyName.Contains(#0)", "Smith")
.Select("Person");
Notes - You will have to add a Contains method to the Dynamic Linq library.
EDIT - Alternatively use just a select...much more simple...but it require the Contains method addition as noted above.
var results = persons.AsQueryable().Where("Names.Select(FamilyName)
.Contains(#0", "Smith)
We originally tried this, but ran into the dreaded 'No applicable aggregate method Contains exists.' error. I a round about way we resolved the problem when trying to get the SelectMany working...therefore just went back to the Select method.
I have an entity and its mapping:
public class Test
{
public virtual int Id { get; set; }
public virtual string Name { get; set; }
public virtual string Description { get; set; }
}
public class TestMap : EntityMap<Test>
{
public TestMap()
{
Id(x => x.Id);
Map(x => x.Name);
Map(x => x.Description);
}
}
I'm trying to run a query on it (to grab it out of the database):
var keyword = "test" // this is coming in from the user
keyword = keyword.ToLower(); // convert it to all lower-case
var results = session.Linq<Test>
.Where(x => x.Name.ToLower().Contains(keyword));
results.Count(); // execute the query
However, whenever I run this query, I get the following exception:
Index was out of range. Must be non-negative and less than the size of the
collection. Parameter name: index
Am I right when I say that, currently, Linq to NHibernate does not support ToLower()? And if so, is there an alternative that allows me to search for a string in the middle of another string that Linq to NHibernate is compatible with? For example, if the user searches for kap, I need it to match Kapiolani, Makapuu, and Lapkap.
I had this happen recently. I can tell you that ToLower() does not work and that Contains() and StartsWith() do work and are not case sensitive. You can get the desired affect by using Contains() and StartsWith() directly.
There seems to be a lot of confusion around this subject.
The "old" Linq provider (for NHibernate 2.x) probably might not support this. If that's the case, it never will because it's not maintained anymore.
The new provider (included with NHibernate 3.x) does support it (although ToUpper and ToLower seem to be inverted, see http://groups.google.com/group/nhibernate-development/browse_thread/thread/a167216e466b3241)
Contains and StartsWith map to the LIKE operator in SQL. They are not case insensitive themselves; it's the collation that makes them case insensitive, so that depends on how your column/schema were created.
Update (2010-04-09): bug confirmed and patch submitted, see https://nhibernate.jira.com/browse/NH-2169
Update (2010-05-21): patch was applied on 2010-05-01 and works as expected now.
According to the comments in these two blog posts this functionality is not implemented yet.
You might want to confirm whether the database uses case sensitivity.
If it doesn't, then you don't need .ToLower()
The accepted answer mentions using Contains() and StartsWith() which are good. but wouldn't work in cases when you want to be sure both strings are the same.
Using "==" will suffice since it is also case-insensitive. So, you no longer need to use ToLower() nor ToUpper();