Today twitting with a colleague, he said me that Groovy is like C# but without LINQ.
I don't know much about LINQ, but I answered him that Groovy has similarities to LINQ, for example, Groovy's class DataSet.
Can you tell me more about similarities / differences between Groovy and LINQ (C#)?
I wonder who told you that ;P
First, let me clarify my statement: Many of the things that I love about c# 4.0 are implemented on groovy, but groovy is already much more succinct.
There are other obvious differences like the dynamic/scripting nature of the groovy language and so forth.
now, linq is a step over closures, like a dsl inside c# to create closures in a query (sql) like sintax, with a pattern based on interfaces and a provider model behind to allow this closures to be translated to sql or to any kind of other representation.
In this respect, since groovy has closures and beautifully implemented, AND it has many dsl-building capabilities built in, it should be possible to make a linq-like feature.
The only similarity between C# and Groovy is their syntax. In other words, Groovy code looks fairly similar to C#. However, the true nature of the languages is very different. Groovy is more like Ruby in that it is dynamically typed and supports meta-programming. C# on the other hand is mostly statically typed.
As for similarities between LINQ and Groovy there are none really. Groovy is a general purpose language, whereas LINQ is a DSL for writing queries. A further difference is that C# and LINQ run on .Net whereas Groovy runs on the JVM.
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I am currently studying Datalog for my report in class, I only need to discuss basic syntax and a basic example.
I know Datalog is usually used as a query language and is usually only implemented to other languages such as Java, Lua, C, etc. but is it possible to teach Datalog only by itself, or am I required to use another language implementing it to show a simple working program?
There are a few online demos you can use:
http://iris-reasoner.org/demo
http://ysangkok.github.io/mitre-datalog.js/wrapper.html
https://repl.logicblox.com/ (docs here:
https://developer.logicblox.com/content/docs4/tutorial/repl/section/split.html )
I haven't tried it myself yet, but http://abcdatalog.seas.harvard.edu also looks nice and easy to run.
A complete overview is on Wikipedia: https://en.wikipedia.org/wiki/Datalog
In Ruby, when you design an embedded DSL a very useful trick is to leverage instance_eval. That way one can offer special statements within a certain block by implementing them as private methods on a special object. This is very nice for contextual stuff.
For an example see: https://robots.thoughtbot.com/writing-a-domain-specific-language-in-ruby
I was wondering what the closest equivalent would be in a Scala EDSL? More specifically how would I offer parts of the syntax only within a certain context that is delimited by a block?
If anybody's wondering: It looks like this is gonna be solve by so-called implicit function types. Here's a good write-up of the idea by Martin Odersky himself: https://www.scala-lang.org/blog/2016/12/07/implicit-function-types.html
Can anyone please help me with a general Entity Framework question? I'm a newbie and trying to teach myself from reading and trial & error. However, I'm getting REALLY confused on all the syntax and terminology. And the more I google, the more confused I get!
What in the world are those little arrows (=>) used in the syntax? And I'm not even sure what the name of the syntax is...is it Entity Framework syntax? Linq to method syntax? Linq to Entity syntax?
Why does it seem like you can use random letters when using that syntax? the "f" below seems interchangeable with any alphabet letter since Intellisense gives me options no matter what letter I type. So what is that letter supposed to stand for anyway? There seems to be no declaration for it.
var query = fruits.SelectMany(f => f.Split(' '));
Is it better to use the syntax with the little arrows or to use the "psuedo SQL" that I keep seeing, like below. This seems a little easier to understand, but is this considered not the Real Entity Framework Way?
var query = from f in fruits from word in f.Split(' ') select word;
And, for any of them - is there any documentation out there ANYWHERE?? I've been scouring the internet for tutorials, articles, anything, but all that comes back are small sample queries varying with the little arrows or that psuedo SQL, with no explanations beyond "here's how to do a select:"
I would much appreciate any guidance or assistance. I think if I can just find out where to start, then I can build myself from there. Thanks!
There is no real entity way, there is LINQ and there is LINQ extension methods which is my opinion is much cleaner to the eyes. Also you can use LINQ not just with EE.
Language Integrated Query
LINQ extends the language by the addition of query expressions, which are akin to SQL statements, and can be used to conveniently extract and process data from arrays, enumerable classes, XML documents, relational databases, and third-party data sources. Other uses, which utilize query expressions as a general framework for readably composing arbitrary computations, include the construction of event handlers2 or monadic parsers.3
1 It is called lambda expression and it is basically an anonymous method.
Exploring Lambda Expression in C#
2 You can use anything you want, word, or letters, anything that is a valid name for a parameter, because that is a parameter
3 I find the LINQ extension methods to be cleaner, and to be honest the last I want to see is SQL like statements laying in the code.
4 A good start can be found here
101 LINQ SAMPLES
The arrow is called a Lambda operator, and it's used to create Lambda expressions. This has nothing to do with EF, or Linq or anything else. It's a feature of C#. EF and Linq just use this feature a lot because it's very useful for writing queries.
Marco has given links to the relevant documentation.
Linq is a library of extension methods that primarily operate on types like IEnumerable and IQueryable interfaces, and give you a lot of power to work with collections of various types. You can write Linq queries either in two formats, so called Method syntax and Query Syntax. They are functionally identical, but their usage is generally a matter of personal preference which one you use (although many of us use both, depending on the context it's used in.. one or the other is easier to use).
Currently I am using LinqKit / Ms dynamic query example to dynamically build Linq Expressions from strings. This works fine.
LinqKit: http://www.albahari.com/nutshell/linqkit.aspx
Microsoft dynamic Linq queries: http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx
Right now, I am migrating my application from C#3.5 to C#4.0. I am wondering if there is another way (standard way of the framework) to build queries from strings.
I have checked the documentation, but did not find anything yet. Also this is not an issue, since I have the above solution.
Only I'd prefer to use the "standard" features if there some. What's the best practice?
I'm currently doing something like this and I'm very happy with the result. The way I did it was with Entity Framework and the ObjectQuery.Select(string query, ObjectParameters[] params) method. More info here: http://msdn.microsoft.com/en-us/library/bb298787.aspx#Y586.
You won't be making expression from string but using SQL to Entities which does the work very well and was made exactly for that purpose as dynamically making Expression isn't trivial and is actually slower.
Cheers
I was thinking about making something like Linq for Lua, and I have a general idea how Linq works, but was wondering if there was a good article or if someone could explain how C# makes Linq possible
Note: I mean behind the scenes, like how it generates code bindings and all that, not end user syntax.
It's hard to answer the question because LINQ is so many different things. For instance, sticking to C#, the following things are involved:
Query expressions are "pre-processed" into "C# without query expressions" which is then compiled normally. The query expression part of the spec is really short - it's basically a mechanical translation which doesn't assume anything about the real meaning of the query, beyond "order by is translated into OrderBy/ThenBy/etc".
Delegates are used to represent arbitrary actions with a particular signature, as executable code.
Expression trees are used to represent the same thing, but as data (which can be examined and translated into a different form, e.g. SQL)
Lambda expressions are used to convert source code into either delegates or expression trees.
Extension methods are used by most LINQ providers to chain together static method calls. This allows a simple interface (e.g. IEnumerable<T>) to effectively gain a lot more power.
Anonymous types are used for projections - where you have some disparate collection of data, and you want bits of each of the aspects of that data, an anonymous type allows you to gather them together.
Implicitly typed local variables (var) are used primarily when working with anonymous types, to maintain a statically typed language where you may not be able to "speak" the name of the type explicitly.
Iterator blocks are usually used to implement in-process querying, e.g. for LINQ to Objects.
Type inference is used to make the whole thing a lot smoother - there are a lot of generic methods in LINQ, and without type inference it would be really painful.
Code generation is used to turn a model (e.g. DBML) into code
Partial types are used to provide extensibility to generated code
Attributes are used to provide metadata to LINQ providers
Obviously a lot of these aren't only used by LINQ, but different LINQ technologies will depend on them.
If you can give more indication of what aspects you're interested in, we may be able to provide more detail.
If you're interested in effectively implementing LINQ to Objects, you might be interested in a talk I gave at DDD in Reading a couple of weeks ago - basically implementing as much of LINQ to Objects as possible in an hour. We were far from complete by the end of it, but it should give a pretty good idea of the kind of thing you need to do (and buffering/streaming, iterator blocks, query expression translation etc). The videos aren't up yet (and I haven't put the code up for download yet) but if you're interested, drop me a mail at skeet#pobox.com and I'll let you know when they're up. (I'll probably blog about it too.)
Mono (partially?) implements LINQ, and is opensource. Maybe you could look into their implementation?
Read this article:
Learn how to create custom LINQ providers
Perhaps my LINQ for R6RS Scheme will provide some insights.
It is 100% semantically, and almost 100% syntactically the same as LINQ, with the noted exception of additional sort parameters using 'then' instead of ','.
Some rules/assumptions:
Only dealing with lists, no query providers.
Not lazy, but eager comprehension.
No static types, as Scheme does not use them.
My implementation depends on a few core procedures:
map - used for 'Select'
filter - used for 'Where'
flatten - used for 'SelectMany'
sort - a multi-key sorting procedure
groupby - for grouping constructs
The rest of the structure is all built up using a macro.
Bindings are stored in a list that is tagged with bound identifiers to ensure hygiene. The binding are extracted and rebound locally where ever an expression occurs.
I did track the progress on my blog, that may provide some insight to possible issues.
For design ideas, take a look at c omega, the research project that birthed Linq. Linq is a more pragmatic or watered down version of c omega, depending on your perspective.
Matt Warren's blog has all the answers (and a sample IQueryable provider implementation to give you a headstart):
http://blogs.msdn.com/mattwar/