Develop Reference

How to fetch data from MongoDB collection in C# using Regular Expression?

I am using MongoDB.Drivers nuget package in my MVC (C#) web application to communication with MongoDB database. Now, I want to fetch data based on specific column and it's value. I used below code to fetch data.
var findValue = "John";
var clientTest1 = new MongoClient("mongodb://localhost:XXXXX");
var dbTest1 = clientTest1.GetDatabase("Temp_DB");
var empCollection = dbTest1.GetCollection<Employee>("Employee");
var builder1 = Builders<Employee>.Filter;
var filter1 = builder1.Empty;
var regexFilter = new BsonRegularExpression(findValue, "i");
filter1 = filter1 & builder1.Regex(x => x.FirstName, regexFilter);
filter1 = filter1 & builder1.Eq(x => x.IsDeleted,false);
var collectionObj = await empCollection.FindAsync(filter1);
var dorObj = collectionObj.FirstOrDefault();
But, the above code is performing like query.
It means it is working as (select * from Employee where FirstName like '%John%') I don't want this. I want to fetch only those data whose FirstName value should match exact. (like in this case FirstName should equal John).
How can I perform this, can anyone provide me suggestions on this.
Note: I used new BsonRegularExpression(findValue, "i") to make search case-insensitive.
Any help would be highly appreciated.
Thanks

I would recommend storing a normalized version of your data, and index/search upon that. It will likely be considerably faster than using regex. Sure, you'll eat up a little more storage space by including "john" alongside "John", but your data access will be faster since you would just be able to use a standard $eq query.
If you insist on regex, I recommend using ^ (start of line) and $ (end of line) around your search term. Remember though, that you should escape your find value so that its contents isn't treated as RegEx.
This should work:
string escapedFindValue = System.Text.RegularExpressions.Regex.Escape(findValue);
new BsonRegularExpression(string.Format("^{0}$", escapedFindValue), "i");
Or if you're using a newer framework version, you can use string interpolation:
string escapedFindValue = System.Text.RegularExpressions.Regex.Escape(findValue);
new BsonRegularExpression($"^{escapedFindValue}$", "i");

Custom string in linq to entity select new

Is there any way to customize it?
This is what Im trying to do:
string customSelect = "c.person_name";
int per = PersonID();
var RetrievItem = (from c in db.person where c.person_id == per select new { customSelect }).FirstOrDefault();
I've tried to debugging it but it just ended up retrieving given string instead of value from database
Any suggestions #_ #?

In addition to Hamlet's comment about an expression based solution, you can have a look at the Dynamic Linq library. It supports lamba expressions defined as strings, which is exactly what you need.

is filter is replaceable of query in mongo queries using c#?

I'm new to mongo in c#
I found tow ways to find documents based on search critiria:
the first using filter:
var collection = _database.GetCollection<BsonDocument>("restaurants");
var filter = Builders<BsonDocument>.Filter.Eq("address.zipcode", "10075");
var result = await collection.Find(filter).ToListAsync();
The second using query:
MongoCollection<BsonDocument> books;
var query = Query.EQ("author", "Kurt Vonnegut");
foreach (BsonDocument book in books.Find(query)) {
// do something with book
}
What's the best way to find documents based to what MongoDB recommendation?

As far I know query builders (like your second example using Query.EQ) belong to old versions of C# drivers (1.X) (see Query class). Also I suggest you to see Builder section in this link that confirm query builders is the old way to consult data.
After the release of the 2.0 version of the .NET driver, a lot of changes were made, including the way of consult the data (you can read more about that in this link). If you are using the last C# driver version you should use your first approach.

The first way you mentioned is quite fine. You might want to incorporate using a mongo cursor as well to allow you to iterate through results
var collection = _database.GetCollection<BsonDocument>("restaurants");
var filter = Builders<BsonDocument>.Filter.Eq("address.zipcode", "10075");
using(var _cursor = await collection.Find(filter).ToCursorAsync())
{
while(await _cursor.MoveNextAsync())
{
foreach(var _document in _cursor.Current) //gets current document
{
//you can do things like get the _id of the document
var _id = _document["_id"];
}
}
}

c# Lambda and grouping

trying to get my head around using Lambda expressions to fetch data from my database.
Say I have a table that looks a bit like this (notice the spaces and casing):
name, count:
iPhone 4, 15
iphone 4, 2
iPhone4, 8
If I try to find items by name (using StartsWith()), I only want to fetch the result with the highest count, independent of casing and spaces. So searches for "iphone4" "i p h o n e 4", "iPhone4" sholud all return the "iPhone 4"-record

If you have a MS Sql Server 2005+ the following would work for your stated example:
var inputString = "iPhone 4";
var token = inputString.ToLower().Replace(" ", "");
var tokenizedQuery = DataContext.Devices.Select(d => new { Device = d, Token = d.Name.ToLower().Replace(" ", "") });
var filteredQuery = tokenizedQuery.Where(d => d.Token == token);
var resultsQuery = filteredQuery.Select(d => d.Device).OrderByDescending(d => d.Count);
var result = resultsQuery.FirstOrDefault();
Here is what is going on:
You are creating a tokenized version of your input string by lower-casing it and then removing spaces.
Then you are creating a pseudo-column on your table to create a similar token column
Filter your results based on this token
Finally, select only the record with the highest count
However it is very important that you realize the ToLower() and Replace() methods are being translated to T-SQL commands that run on the sql server and not in your app. This means should you need more sophisticated tokenizing routines, or you are not using MS SQL this may not work!
As others have noted, you may want to clean up your design somewhat. You are essentially storing a key or search keyword that can have many permutations. Doing the tokenizing in a query is not portable or performant, so you should ideally store the tokenized version of this string in its own column. Alternatively, look into Full Text Indexes, as they may also address your problem (again, if using MSSQL).

Let's assume that you have a Collapse string extension, which is not hard to write. One thing you'll note is that there won't be a mapping from this to SQL so the final filtering will have to be done in LINQ to Objects. You might be able to make the DB query more efficient by doing partial filtering (i.e., on iphone), then complete the filtering in memory.
db.Table.ToList().Where( t => t.Name.Collapse().StartsWith( searchString.Collapse() )
.OrderByDescending( t => t.Count )
.Take( 1 );
Where Collapse is
public static class StringExtensions
{
public static string Collapse( this string source )
{
if (string.IsNullOrWhiteSpace( source ))
{
return string.Empty;
}
var builder = new StringBuilder();
foreach (char c in source)
{
if (!char.IsWhiteSpace( c ))
{
builder.Append( c );
}
}
return builder.ToString();
}
}
Note: you'd be better off sanitizing your database if possible AND you really want these to map to the same thing.

MongoDB and C#: Case insensitive search

I am using MongoDB and the C# driver for MongoDB.
I recently discovered that all queries in MongoDB are case-sensitive. How can I make a case-insensitive search?
I found one way to do this:
Query.Matches(
"FirstName",
BsonRegularExpression.Create(new Regex(searchKey,RegexOptions.IgnoreCase)));

The simplest and safest way to do that is using Linq:
var names = namesCollection.AsQueryable().Where(name =>
name.FirstName.ToLower().Contains("hamster"));
As explained in the tutorial ToLower, ToLowerInvariant, ToUpper and ToUpperInvariant all perform matches in a case insensitive way. After that you can use all the supported string methods like Contains or StartsWith.
This example will generate:
{
"FirstName" : /hamster/is
}
The i option makes it case insensitive.

I've just implemented this much simpler than any of the other suggestions. However I realise due to the age of this question, this functionality may not have been available at the time.
Use the options of the Bson Regular Expression constructor to pass in case insensitivity. I just had a look at the source code and found that 'i' is all you need. For example.
var regexFilter = Regex.Escape(filter);
var bsonRegex = new BsonRegularExpression(regexFilter, "i");
Query.Matches("MyField", bsonRegex);
You shouldn't have to keep records twice for searching.

try to use something like this:
Query.Matches("FieldName", BsonRegularExpression.Create(new Regex(searchKey, RegexOptions.IgnoreCase)))

You will probably have to store the field twice, once with its real value, and again in all lowercase. You can then query the lowercased version for case-insensitive search (don't forget to also lowercase the query string).
This approach works (or is necessary) for many database systems, and it should perform better than regular expression based techniques (at least for prefix or exact matching).

As i3arnon answered, you can use Queryable to do a case insensitive comparison/search. What i found out was, that i could not use string.Equals() method, because is it not supported. If you need to do a comparison, Contains() will unfortunately not be suitable which kept me struggling for a solution, for quite some time.
For anyone wanting to do a string comparison, simply use == instead of .Equals().
Code:
var names = namesCollection.AsQueryable().Where(name =>
name.FirstName.ToLower() == name.ToLower());

For MongoDB 3.4+ the recommended way is to use indexes.
See https://jira.mongodb.org/browse/DOCS-11105?focusedCommentId=1859745&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-1859745
I am successfully searching with case insensitive by:
1. Creating an index with Collation for a locale (e.g: "en") and with a strength of 1 or 2. See https://docs.mongodb.com/manual/core/index-case-insensitive/ for further details
Using the same Collation when performing searches on the MongoDb collection.
As an example:
Create a collation with strength 1 or 2 for case insensitive
private readonly Collation _caseInsensitiveCollation = new Collation("en", strength: CollationStrength.Primary);
Create an index. In my case I index several fields:
private void CreateIndex()
{
var indexOptions = new CreateIndexOptions {Collation = _caseInsensitiveCollation};
var indexDefinition
= Builders<MyDto>.IndexKeys.Combine(
Builders<MyDto>.IndexKeys.Ascending(x => x.Foo),
Builders<MyDto>.IndexKeys.Ascending(x => x.Bar));
_myCollection.Indexes.CreateOne(indexDefinition, indexOptions);
}
When querying make sure you use the same Collation:
public IEnumerable<MyDto> GetItems()
{
var anyFilter = GetQueryFilter();
var anySort = sortBuilder.Descending(x => x.StartsOn);
var findOptions = new FindOptions {Collation = _caseInsensitiveCollation};
var result = _salesFeeRules
.Find(anyFilter, findOptions)
.Sort(anySort)
.ToList();
return result;
}

You can also use MongoDB's built in filters. It may make it easier for using some of mongo's methods.
var filter = Builders<Model>.Filter.Where(p => p.PropertyName.ToLower().Contains(s.ToLower()));
var list = collection.Find(filter).Sort(mySort).ToList();

The easiest way for MongoDB 3.4+ is to use one of ICU Comparison Levels
return await Collection()
.Find(filter, new FindOptions { Collation = new Collation("en", strength: CollationStrength.Primary) })
.ToListAsync();
More info https://docs.mongodb.com/manual/reference/method/cursor.collation/index.html

In case anyone else wondering, using fluent-mongo add-on, you can use Linq to query like that:
public User FindByEmail(Email email)
{
return session.GetCollection<User>().AsQueryable()
.Where(u => u.EmailAddress.ToLower() == email.Address.ToLower()).FirstOrDefault();
}
Which results in correct JS-query. Unfortunately, String.Equals() isn't supported yet.

A way to do it is to use the MongoDB.Bson.BsonJavaScript class as shown below
store.FindAs<Property>(Query.Where(BsonJavaScript.Create(string.Format("this.City.toLowerCase().indexOf('{0}') >= 0", filter.City.ToLower()))));

this is exact text search and case insensitive (see this link).
{ “FieldName” : /^keywordHere$/i }