The problem I have with the various ORM modules available for databases like MySQL and MongoDB is the inability to keep model information coupled with the database itself.
I want to be able to add a model to my ORM setup at runtime via an administrative HTTP interface and give it some fields that may be ascribed to various predefined data types (like 'email' or 'telephone number'). Possibly the most contentious feature I'm after is the ability to cast a field as a data type that has already been previously defined by the user as a model.
Is this just me trying to have my cake and eat it? Can anybody see a way of implementing something like this? All the ORM modules I've seen so far simply require instantiating models at application level, essentially before runtime.
It's probably worth mentioning I'm hoping to implement this in a Node environment (not a classic LAMP setup).
EDIT:
I take it from the lack of community bite that I may have stumbled back into the Object-Relational Impedance Mismatch issue here?
If your solution depends on multiple drivers, you can try light-orm. It is simple wrapper for relations dbs.
Related
I'm writing a web application using PHP/Symfony2/Doctrine2 and just finishing up the design of the Database. We have to import these objects (for ex. Projects, Vendors) into our database that come from different customers with variety of fields. Some customers have 2 fields in the project object and some have 20. So I was thinking about implementing them in MongoDB since it seems like a good use for it.
Symfony2 supports both ORM and ODM so that shouldn't be a problem, Now my question is how to ensure the integrity of the data in both databases. Because Objects in my MySQL db need to somehow be linked to the objects in the MongoDB for integrity issues.
Are there any better solutions out there? Any help/thoughts would be appreciated
Bulat implemented a Doctrine extension while we were at OpenSky for handling references between MongoDB documents and MySQL records, which is currently sitting in their (admittedly outdated) fork of the DoctrineExtensions project. You'll want to look at either the orm2odm_references or openskyfork branches. For this to be usable in your project, you'll probably want to port it over to a fresh fork of DoctrineExtensions, or simply incorporate the code into your application. Unfortunately, there is no documentation apart from the code itself.
Thankfully, there is also cookbook article on the Doctrine website that describes how to implement this from scratch. Basically, you rely on an event listener to replace your property with a reference (i.e. uninitialized Proxy object) from the other object manager and the natural behavior of Proxy objects to lazily load themselves takes care of the rest. Provided the event listener is a service, you can easily inject both the ORM and ODM object managers into it.
The only integrity guaranteed by this model is that you'll receive exceptions when trying to hydrate a bad reference, which is probably more than you'd get by simply storing an ID of the other database and querying manually.
So the way we solved this problem was by moving to Postgres. Postgres has a datatype called hstore that acts like a NoSQL column. Works pretty sweet
UPDATE
Now that I'm looking back, go with jsonb instead of json or hstore as it allows you to have more of a data structure than a key-value store.
i was asked to do a book manager at university with hibernate and mysql. I have a simple question. If i choose to do a web application, grails already uses hibernate. GORM runns over hibernate. so to use mysql i only need to configure jdbc grails drivers and that's it?
i mean, "for the project you must use hibernate and mysql" - this are the requirements. So can i do that way?
thanks in advance,
JM
Yes, of course you can.
You'll need to get the MySQL JDBC driver from this location.
Grails? When you're new to programming? Whose idea was this?
Personally, I think that taking on all these unknowns is risky for someone who's "new to programming." Do you know anything about SQL or JDBC? Have you ever written a web project before? This could be difficult.
I don't know how to be more specific. Download the JDBC JAR from the link I gave you.
I'd recommend that you start with a JDBC tutorial first. Hibernate is not for you - yet.
Hibernate is an object-relational mapping tool (ORM). It's a technology that lets you associate information in relational database tables to objects in your middle tier. So if you have a PERSON table with columns id, first, and last Hibernate will let you associate those data with the private data members in your Person Java class.
That sounds easy, but it gets complicated quickly. Your relational and object models might have one-to-many and many-to-many relationships; Hibernate can help with those. Lazy loading, caching, etc. can be managed by Hibernate.
But it comes at a cost. And it can be difficult if you aren't familiar with it.
If you have a deadline, I'd recommend creating a Java POJO interface for your persistence classes and doing the first implementation using JDBC. If you want to swap it out for Hibernate later on you can do it without affecting clients, but you'll have a chance of making progress without Hibernate that way.
I'm trying to familiarize myself a bit more with database programming, and I'm looking at different ways of creating a data access layer for applications. I've tried out a few ways but there is such a jungle of different database technologies that I don't know what to learn. For instance I've tried using datasets with tableadapters. Using that I am able to switch data provider rather easily (by programming against the interfaces such as IDbConnection). This is one thing I would want to achieve. But I also know everyone's talking about LINQ, and I'm trying to get to know that a bit better too. So I have tried using Linq to Sql classes as the data access layer as well, but apparently this is not provider independent (works only for SQL Server).
So then I read about the Entity Framework (which just as Linq to SQL apparently has gotten its share of bashing already...). It's supposed to be provider independent everybody says, but how? I tried out a tutorial to create an entity data model, but the only providers to choose from were SQL Server/Express. Just for learning purposes, I would like to know how to use the entity framework with MS Access/OleDb.
Also, I would appreciate some input on what is the preferred database technology for data access. Is it LINQ still after all the bashing, or should you just use datasets because they are provider independent? Any pointers for what to learn would be great, because it's just too much to learn it all if I'm not going to use it in the end...!
the only providers to choose from were SQL Server/Express
The .NET Framework only includes EF providers for SQL Server and SQL Server Compact. If you need to access another DBMS, you need to install a third-party provider. For instance, there's a free provider for SQLite, with designer support. There are also a few (commercial) providers made by Devart, for various DBMS. As far as I know, there are no EF providers for OleDB or ODBC...
I really like the metaphor from Scott Hanselman: "I'm not a plumber, but I do know what an S-Bend is."
Personally, I think you should have a working knowledge of all the variety of ways to access data.
ADO.Net, EF, Linq2Sql, txt files, xml etc etc etc.
Have a look at the Nerd Dinner and the Music Store samples. See the way they access data (how do they do Unit Tests, Mocking framework, IOC etc)
Regarding data providers, personally I would avoid Access. It is just as easy to get a Sql Express or Mysql installation running and looks better on your resume.
(For what its worth, this question discusses setting up mysql for EF.)
I'm going to start a new project which is going to be small initially but may grow to big over the years. I'm strongly convinced that I'm going to use ASP.NET MVC with jQuery for UI. I want to go for MySQL as database for some reasons but worried on few things.
I'm totally new to Linq but it seems that it is easier to use once you are familiar with it.
First thing is that accessing data should be easy. So I thought I should use MySQL to Linq but somewhere I read that it is not directly supported but MySQL .NET connector adds support for EntityFramework. I don't know what are the pros and cons of it. DbLinq is what I also heard. I would love if I can implement repository pattern as it allows to apply filter in logic layer rather than in data access layer. Will it be possible if I use Entity Framework?
I'm also concerned about the performance. Someone told me that if we use Entity framework it fetches lot of data and then filter it. Is that right?
So questions basically are -
Is MySQL to Linq possible? If yes where can I get more details on it?
Pros and cons of using EntityFramework or DbLinq with MySQL?
Will it be easy to access data using EntityFramework or DbLinq with MySQL?
Will I be able to implement repository pattern which allows applying filter in logic layer rather than data access layer (when I use EntityFramework with MySQL)
Does it fetches hell lot of data from database and then apply filter on it?
If it sounds too many questions from my side in that case, if you can just let me know what you will do (with a considerable reason) in this situation as an experienced person in this area, that should answer my question.
As I am fan of ALT.NET I would recomend you to use NHibernate for your project instead of EntityFramework, you may google for the advantages over it, I am convinced you'll choose it.
Based on the points you've mentioned, then I would seriously consider going with MS SQL instead of MySQL initially and implementing LINQ-to-SQL instead of Entity Framework, and here's why:
The fact that you are anticipating a lot of traffic initially tells me that you need to think about where you plan to end up, rather than where to start. I have considerably more experience with MS SQL than I do with MySQL, but if you're talking about starting with the community version of MySQL and upgrading later, you're going to be incurring a significant expense anyway with the Enterprise version.
I have heard there is a version of LINQ that supports MySQL, but, unless things have changed recently, it is still in beta. I am completing an 18-month web-based project that used ASP.NET MVC 1.0, LINQ-to-SQL, JavaScript, jQuery, AJAX, and MS SQL. I implemented the repository pattern, view models, interfaces, unit tests and integration tests using WatiN. The combination of technologies worked very well for me, and I plan to go with the same combination for a personal project I'm developing.
When you get MS SQL with a hosting plan, you typically have the ability to create multiple databases from that single instance. It looks like they give you more storage because they give you multiple MySQL databases, but that's only because the architecture only supports the creation of one database per instance.
I won't use the Entity Framework for my ASP.NET MVC projects, because I wasn't crazy about ADO.NET in the first place. I don't want to have to open a connection, create a command object, populate a parameter collection, issue the execute method, and then iterate through a one-way reader object to get my data. Once you see how LINQ-to-SQL simplifies the process, you won't want to go back either. In the project I mentioned earlier, I have over 60 tables in the database with about 200 foreign key relationships. Because I used LINQ-to-SQL with the repository pattern in my data layer, I was able to build the application using not a single stored procedure. LINQ-to-SQL automatically protects against SQL injection attacks and support optimistic and pessimistic concurrency checking.
I don't know what your project is, but you don't want to get into a situation where you're going to have trouble scaling the application later. Code for the end result, not for the starting point, and you'll save yourself a lot of headaches later.
First a bit about the environment:
We use a program called Clearview to manage service relationships with our customers, including call center and field service work. In order to better support clients and our field technicians we also developed a web site to provide access to the service records in Clearview and reporting. Over time our need to customize the behavior and add new features led to more and more things being tied to this website and it's database.
At this point we're dealing with things like a Company being defined partly in the Clearview database and partly in the website database. For good measure we're also starting to tie the scripting for our phone system into the same website, which will require talking to the phone system's own database as well.
All of this is set up and working... BUT we don't have a good data layer to work with it all. We moved to Linq to SQL and now have two DBMLs that we can use, along with some custom classes I wrote before I'd ever heard of Linq, along with some of the old style ADO datasets. So yeah, basically things are a mess.
What I want is a data layer that provides a single front end for our applications, and on the back end manages everything into the correct database.
I had heard something about Entity Framework allowing classes to be built from multiple sources, but it turns out there can only be one database. So the question is, how could I proceed with this?
I'm currently thinking of getting the Linq To SQL classes all set for each database, then manually writing Linq compatible front ends that tie those together. Seems like a lot of work, and given Linq's limitations (such as not being able to refresh) I'm not sure it's a good idea.
Could I do something with Entity Framework that would turn out better? Should I look into another tool? Am I crazy?
The Entity Framework does give a certain measure of database independence, insofar as you can build an entity model from one database, and then connect it to a different database by using a different entity connect string. However, as you say, it's still just one database, and, moreover, it's limited to databases which support the Entity Framework. Many do, but not all of them. You could use multiple entity models within a single application in order to combine multiple databases using the Entity Framework. There is some information on this on the ADO.NET team blog. However, the Entity Framework support for doing this is, at best, in an early stage.
My approach to this problem is to abstract my use of the Entity Framework behind the Repository pattern. The most immediate benefit of this, for me, is to make unit testing very simple; instead of trying to mock my Entity model, I simply substitute a mock repository which returns IQueryables. But the same pattern is also really good for combining multiple data sources, or data sources for which there is no Entity Framework provider, such as a non-data-services-aware Web service.
So I'm not going to say, "Don't use the Entity Framework." I like it, and use it, myself. In view of recent news from Microsoft, I believe it is a better choice than LINQ to SQL. But it will not, by itself, solve the problem you describe. Use the Repository pattern.
if you want to use tools like Linq2SQl or EF and don't want to have to manage multiple DBMLS (or whaetever its called in EF or other tools), you could create views in your website database, that reference back to the ClearView or Phone system's DB.
This allows you to decouple your web site from their database structure. I believe Linq2Sql and EF can use a view as the source for an Entity. If they can't look at nHibernate.
This will also let you have composite entities that are pulled from the various data sources. There are some limitations updating views in SQL Server; however, you can define your own Instead of trigger(s) on the view which can then do the actual insert update delete statements.
L2S works with views, perfectly, in my project. You only need to make a small trick:
1. Add a secondary DB table to the current DB as a view.
2. In Designer, add a primary key attribute to a id field on the view.
3. Only now, add an association to whatever other table you want in the original DB.
Now, you might see the view available for the navigation.