I am currently working on a project where I have to retrieve some rows from the database based on some filters (I also have to paginate them).
My solution was to make a function that generates the queries and to query the database directly (it works and it's fast)
When I presented this solution to the senior programmer he told me this is going to work but it's not a long-term solution and I should rather use Spring Specifications.
Now here comes my questions :
Why is Spring Specifications better than generating a query?
Is a query generated by Spring Specifications faster than a normal query?
Is it that big of a deal to use hard-coded queries ?
Is there a better approach to this problem ?
I have to mention that the tables in the database don't store a lot of data, the biggest one (which will be queried the least) has around 134.000 rows after 1 year since the application was launched.
The tables have indexes on the rows that we will use to filter.
A "function that generates the queries" sounds like building query strings by concatenating smaller parts based on conditions. Even presuming this is a JPQL query string and not a native SQL string that would be DB dependent, there are several problems:
you lose the IDEs help if you ever refactor your entities
not easy to modularize and reuse parts of the query generation logic (eg. if you want to extract a method that adds the same conditions to a bunch of different queries with different joins and aliases for the tables)
easy to break the syntax of the query by a typo (eg. "a=b" + "and c=d")
more difficult to debug
if your queries are native SQL then you also become dependent on a database (eg. maybe you want your integration tests to run on an in-memory DB while the production code is on a regular DB)
if in your project all the queries are generated in a way but yours is generated in a different way (without a good reason) then maintenance of the will be more difficult
JPA frameworks generate optimized queries for most common use cases, so generally speaking you'll get at least the same speed from a Specification query as you do from a native one. There are times when you need to write native SQL to further optimize a query but these are exceptional cases.
Yes, it's bad practice that makes maintenance a nightmare
I have multiple migrations (say around 10) and the corresponding models for the tables. The problem I am facing is that all the migrations/tables have multiple primary keys but the model has just a string variable to define primary key ($primaryKey), hence, when I save or update a table row using where clause it would just take one primary key and miss the other and hence end up changing multiple rows instead of one. So, basically I switched to DB Queries and it worked well.
So, my question to you is that is there any performance gain with model? Or it is just a designing paradigm? Is there any option to do the same thing (Have multiple primary key) within a model? I know by overriding the Eloquent methods we can do this but is there any other good option?
Using an ORM like Eloquent is a convenience, not a requirement. From what I've heard there's actually often a slight performance decrease when using an ORM because there's the additional overhead of translating that query into the relevant SQL.
Often, using an ORM makes for queries that are much easier to understand, and for that reason alone it's worth using. However, for more complex queries, an ORM is likely to get in the way, and so you should consider using another method to query the database. You don't have to use just an ORM - you can mix and match the different methods as you see fit.
Laravel has the Query Builder as an alternative to writing raw SQL or using the ORM, and that may be a better option for you here. I would avoid writing raw SQL if you can because both Eloquent and the Query Builder will handle escaping the parameters for you, to help avoid SQL injection vulnerabilities.
My choice would be to use the ORM where possible, and fall back to the Query Builder when the ORM gets in the way.
I'm not so good at both Linq and SQL. But I have worked more with SQL and less with LINQ. I've gone through many articles which favors LINQ. I don't want to go the SQL way (i.e. writing stored procedures and operating data etc.)
I want to start with LINQ for every operation related with data. Here are the reasons why I want to do this:
I want to have complete control of my database via application and not by writing stored procs (as I'm not so good at writing store procedure)
I want to create my project as an easy maintainability view
Want faster development
For that, I know that:
I need to add a dbml file, drag and drop tables into that
Use dbContext class, and so on
But I want to know, is there a way:
I can avoid creating dbml file and still be able to access the database?
Do I need to use Linq to Entities for the same?
Will it be a good way to avoid using dbml file? Since for every database changes I need to drop and drop tables every time
Also I've come across many posts where linqToSql is considered deprecated and not a .net future?
I have so many doubts, but I think that's obvious when starting with a new technology?
I found this useful article which is good for beginners:
[http://weblogs.asp.net/scottgu/archive/2010/08/03/using-ef-code-first-with-an-existing-database.aspx][1]
after doing some more research I came to conclusion that:
1)i can avoid creating dbml file and still be able to access database??
ANS Yes but instead of dbml now edmx files will be created.
2)Do I need to use Linq to Entities for the same?
ANS Yes you can go with linq to entities.
3)Will it be good way avoid using dbml file? since for every database changes I need to drop and drop tables every time
ANS it is not required to drop and create again the tables. their are options where you can update selected part of your database and you are not avoiding dbmls. it will created edmx file and that will almost similar to dbmls in many ways.
4) Also I've come across many posts where linqToSql is considered deprecated and not a .net future?
ANS yes in future development it will be depreciated. it supports only sql server as backend.
I hope I'm right. Please do tell me in case any other suggestions.
LINQ is a way to query and project collection of data. For example, you can use LINQ to query and shape data from a database or from an array. LINQ by it self has nothing to with the under lying database.
You use an ORM (Object Relational Mapper) technology to project data stored in tables of a database as collections of objects. Once you have the collection of objects, you can use LINQ to query them.
Now, you have many ORM technologies to select from, such as Entity Framework, NHibernate, Linq2Sql. If you don’t like to maintain a dbml file, have a look at code first approach offered by Entity Framework.
Then there are things called LINQ data providers. They would take a LINQ query, transform it to a SQL targeting a particular database, execute the query and get the results back as a set of objects. Many of the ORMs above has built in LINQ data providers as a part of them and would work behind the scene in fetching the data.
I would advise you to look up on some patterns such Repository and Unit of work for your data layer. When used correctly, these patterns will isolate your data access code from your applications upper layers. This will help you to change your data access technology is it becomes obsolete, without affecting the rest of the application.
LINQ is an awesome technology and you should definitely try it
I have composed the above answer based on my own experience and I am sure there are many SO users with better understanding of the above technologies than myself who may wish to add their own opinion
Good luck
I have an MVC3 NHibernate/ActiveRecord project. The project is going okay, and I'm getting a bit of use out of my model objects (mostly one giant hierarchy of three or four classes).
My application is analytics based; I store hierarchial data, and later slice it up, display it in graphs, etc. so the actual relationship is not that complicated.
So far, I haven't benefited much from ORM; it makes querying easy (ActiveRecord), but I frequently need less information than full objects, and I need to write "hard" queries through complex and multiple selects and iterations over collections -- raw SQL would be much faster and cleaner.
So I'm thinking about ditching ORM in this case, and going back to raw SQL. But I'm not sure how to rearchitect my solution. How should I handle the database tier?
Should I still have one class per model, with static methods to query for objects? Or should I have one class representing the DB?
Should I write my own layer under ActiveRecord (or my own ActiveRecord-like implementation) to keep the existing code more or less sound?
Should I combine ORM methods (like Save/Delete) into my model classes or not?
Should I change my table structure (one table per class with all of the fields)?
Any advice would be appreciated. I'm trying to figure out the best architecture and design to go with.
Many, including myself, think the ActiveRecord pattern is an anti-pattern mainly because it breaks the SRP and doesn't allow POCO objects (tightly coupling your domain to a particular ORM).
In saying that, you can't beat an ORM for simple CRUD stuff, so I would keep some kind of ORM around for that kind of work. Just re-architect your application to use POCO objects and some kind or repository pattern with your ORM implementation specifics in another project.
As for your "hard" queries, I would consider creating one class per view using a tiny ORM (like Dapper, PetaPoco, or Massive), to query the objects with your own raw sql.
As someone who hasn't used either technology on real-world projects I wonder if anyone knows how these two complement each other and how much their functionalities overlap?
LINQ to SQL forces you to use the table-per-class pattern. The benefits of using this pattern are that it's quick and easy to implement and it takes very little effort to get your domain running based on an existing database structure. For simple applications, this is perfectly acceptable (and oftentimes even preferable), but for more complex applications devs will often suggest using a domain driven design pattern instead (which is what NHibernate facilitates).
The problem with the table-per-class pattern is that your database structure has a direct influence over your domain design. For instance, let's say you have a Customers table with the following columns to hold a customer's primary address information:
StreetAddress
City
State
Zip
Now, let's say you want to add columns for the customer's mailing address as well so you add in the following columns to the Customers table:
MailingStreetAddress
MailingCity
MailingState
MailingZip
Using LINQ to SQL, the Customer object in your domain would now have properties for each of these eight columns. But if you were following a domain driven design pattern, you would probably have created an Address class and had your Customer class hold two Address properties, one for the mailing address and one for their current address.
That's a simple example, but it demonstrates how the table-per-class pattern can lead to a somewhat smelly domain. In the end, it's up to you. Again, for simple apps that just need basic CRUD (create, read, update, delete) functionality, LINQ to SQL is ideal because of simplicity. But personally I like using NHibernate because it facilitates a cleaner domain.
Edit: #lomaxx - Yes, the example I used was simplistic and could have been optimized to work well with LINQ to SQL. I wanted to keep it as basic as possible to drive home the point. The point remains though that there are several scenarios where having your database structure determine your domain structure would be a bad idea, or at least lead to suboptimal OO design.
Two points that have been missed so far:
LINQ to SQL does not work with Oracle
or any database apart from SqlServer. However 3rd parties do offer better support for Oracle, e.g. devArt's dotConnect, DbLinq, Mindscape's LightSpeed and ALinq. (I do not have any personal experience with these)
Linq to NHibernate lets you used
Linq with a Nhiberate, so it may
remove a reason not to use.
Also the new fluent interface to Nhibernate seems to make it less painful to configure Nhibernate’s mapping. (Removing one of the pain points of Nhibernate)
Update
Linq to Nhiberate is better in Nhiberate v3 that is now in alpha. Looks like Nhiberate v3 may ship towards the end of this year.
The Entity Frame Work as of .net 4 is also starting to look like a real option.
#Kevin: I think the problem with the example you are presenting is that you are using a poor database design. I would have thought you'd create a customer table and an address table and normalized the tables. If you do that you can definately use Linq To SQL for the scenario you're suggesting. Scott Guthrie has a great series of posts on using Linq To SQL which I would strongly suggest you check out.
I don't think you could say Linq and NHibernate complement each other as that would imply that they could be used together, and whilst this is possible, you're much better off choosing one and sticking to it.
NHibernate allows you to map your database tables to your domain objects in a highly flexible way. It also allows you to use HBL to query the database.
Linq to SQL also allows you to map your domain objects to the database however it use the Linq query syntax to query the database
The main difference here is that the Linq query syntax is checked at compile time by the compiler to ensure your queries are valid.
Some things to be aware of with linq is that it's only available in .net 3.x and is only supported in VS2008. NHibernate is available in 2.0 and 3.x as well as VS2005.
Some things to be aware of with NHibernate is that it does not generate your domain objects, nor does it generate the mapping files. You need to do this manually. Linq can
do this automatically for you.
Fluent NHibernate can generate your mapping files based on simple conventions. No XML-writing and strongly typed.
I've recently worked on a project, where we needed to change from Linq To SQL to NHibernate for performance reasons. Especially L2S's way of materializing the objects seems slower than NHibernate's ditto and the change management is quite slow too. And it can be hard to turn the change management off for specific scenarios where it is not needed.
If you are going to use your entities disconnected from the DataContext - in WCF scenarios for example - you're may have a lot of trouble connecting them to the DataContext again for updating the changes. I have had no problems with that with NHibernate.
The thing I will miss from L2S is mostly the code generation that keeps relations up-to-date on both ends of the entities. But I guess there are some tools for NHibernate to do that out there too...
Can you clarify what you mean by "LINQ"?
LINQ isn't an data access technology, it's just a language feature which supports querying as a native construct. It can query any object model which supports specific interfaces (e.g. IQueryable).
Many people refer to LINQ To SQL as LINQ, but that's not at all correct. Microsoft has just released LINQ To Entities with .NET 3.5 SP1. Additionally, NHibernate has a LINQ interface, so you could use LINQ and NHibernate to get at your data.
By LINQ, I'm assuming you mean LINQ to SQL because LINQ, by itself, has no database "goings on" associated with it. It's just an query language that has a boat-load of syntac sugar to make it look SQL-ish.
In the very basic of basic examples, NHibernate and LINQ to SQL seem to both be solving the same problem. Once you get pass that you soon realize that NHibernate has support for a lot of features that allow you to create truly rich domain models. There is also a LINQ to NHibernate project that allows you to use LINQ to query NHibernate in much the same way as you would use LINQ to SQL.
First let´s separate two different things:
Database modeling is concerned about the data while object modeling is concerned about entities and relationships.
Linq-to-SQL advantage is to quickly generate classes out of database schema so that they can be used as active record objects (see active record design pattern definition).
NHibernate advantage is to allow flexibility between your object modeling and database modeling. Database can be modeled to best reflect your data taking in consideration performance for instance. While your object modeling will best reflect the elements of the business rule using an approach such as Domain-Driven-Design. (see Kevin Pang comment)
With legacy databases with poor modeling and/or naming conventions then Linq-to-SQL will reflect this unwanted structures and names to your classes. However NHibernate can hide this mess with data mappers.
In greenfield projects where databases have good naming and low complexity, Linq-to-SQL can be good choice.
However you can use Fluent NHibernate with auto-mappings for this same purpose with mapping as convention. In this case you don´t worry about any data mappers with XML or C# and let NHibernate to generate the database schema from your entities based on a convention that you can customize.
On the other hand learning curve of Linq-to-SQL is smaller then NHibernate.
Or you could use the Castle ActiveRecords project. I've been using that for a short time to ramp up some new code for a legacy project. It uses NHibernate and works on the active record pattern (surprising given its name I know). I haven't tried, but I assume that once you've used it, if you feel the need to drop to NHibernate support directly, it wouldn't be too much to do so for part or all of your project.
As you written "for a person who have not used either of the them"
LINQ to SQL is easy to use so any one can use it easily
It also support procedures, which helps most of the time.
Suppose you want to get data from more than one table then write a procedure and drag that procedure to designer and it will create everything for you,
Suppose your procedure name is "CUSTOMER_ORDER_LINEITEM" which fetch record from all these three table then just write
MyDataContext db = new MyDataContext();
List<CUSTOMER_ORDER_LINEITEMResult> records = db.CUSTOMER_ORDER_LINEITEM(pram1, param2 ...).ToList<CUSTOMER_ORDER_LINEITEMResult>();
you can use you records object in foreach loop as well, which is not supported by NHibernate