Introduction to DataContext and DataSet - database

Can anyone help me understand DataContext and DataSet ? I am leaning Entity Framework and I need to clear this concepts in my mind properly.
I tried to read in the book, read some articles but all the language there was so complex, can anyone explain me these terms using simple words with example?
Also if you can provide me the link of any video tutorials that could help me.
Thanks.

DbContext and DbSet are two classes that when you use EF code first approach, you can work with them.
Using Entity Framework you can simply define a mapping between your entities and tables.
In simple words, you can imagine DbContext as an In-Memory database, and DataSets as In-Memory tables(that initially are empty), you can imagine entity objects as rows of your tables in your database, too:
In your application you can query DbSets or do CUD(Creat,Update,Delete) operations on them instead direct access to your database and tables. You could execute multiple CRUD operations on DbSets, in simple database transaction, too.

Related

Managing multiple datasources in CakePHP

I'm planning to develop a web application in CakePHP that shows information in graphics and cards. I chose CakePHP because the information that we need to show is very structured, so the model approach makes easier to manage data; also I have some experience with MVC from ASP.NET and I like how simple is to use the routing.
So, my problem is that the multiple organizations that could use the app would have their own database with a different schema that the one we need. I can't just set their string connection in the app.php file because their database won't match my model.
And the organization datasource couldn't fit my model for a lot of reasons: the tables don't have the same name, the schema is different, the fields of my entity are in separated tables, maybe they have the info in different databases or also in different DBMS!
I want to know if there's a way to make an interface that achieves this
In such a way that cakephp Model/Entity can use data regardless of the source. Do you have any suggestions of how to do that? Does CakePHP have an option to make this possible? Should I use PHP with some kind of markup language like JSON or XML? Maybe MySQL has an utility to transform data from different sources into a view and I can make CakePHP use the view instead of the table?
In case you have an answer be as detailed as you can.
This other options are possible if it's impossible to make the interface:
- Usw another framework that can handle this easier and has the features I mentioned above.
- Make the organization change their database so it matches my model (I don't like this one, and probably they won't do it).
- Transfer the data in the application own database.
Additional information:
The data shown in graphics are from students in university. Any university has its own database with their own structure and applications using the db, that's why isn't that easy to change structure. I just want to make it as easy as possible to any school to configure their own db.
EDIT:
The version is CakePHP 3.2.
An important appointment is that it doesn't need all CRUD operations, only "reading". Hope that makes the solution easier.
I don't think your "question" can be answered properly, it doesn't contain enough information, not enough details. I guess there is something that will stay the same for all organizations but their data and business logic will be different. But I'll try it.
And the organization datasource couldn't fit my model for a lot of reasons: the tables don't have the same name, the schema is different, the fields of my entity are in separated tables, maybe they have the info in different databases or also in different DBMS!
Model is a whole layer, so if you have completely different table schemas your business logic, which is part of that layer, will be different as well. Simply changing the database connection alone won't help you then. The data needs to be shown in the views as well and the views must be different as well then.
So what you could try to do and what your 2nd image shows is, that you implement a layer that contains interfaces and base classes. Then create a Cake plugin for each of the organizations that uses these interfaces and base classes and write some code that will conditionally use the plugin depending on whatever criteria (guess domain or sub-domain) is checked. You will have to define the intermediate interfaces in a way that you can access any organization the same way on the API level.
And one technical thing: You can define the connection of a table object in the model layer. Any entity knows about it's origin but you should not implement business logic inside an entity nor change the connection through an entity.
EDIT: The version is CakePHP 3.2. An important appointment is that it doesn't need all CRUD operations, only "reading". Hope that makes the solution easier.
If that's true either use the CRUD plugin (yes, you can use only the R part of it) or write some code, like a class that describes the organization and will be used to create your table objects and views on the fly.
Overall it's a pretty interesting problem but IMHO to broad for a simple answer or solution that can be given here. I think this would require some discussion and analysis to find the best solution. If you're interested in consulting you can contact me, check my profile.
I found a way without coding any interface. In fact, it's using some features already included in the DBMS and CakePHP.
In the case that the schema doesn't fit the model, you can create views to match de table names and column names from the model. By definition, views work as a table so CakePHP searches for the same table name and columns and the DBMS makes the work.
I made a test with views in MySQL and it worked fine. You can also combine the data from different tables.
MySQL views
SQL Server views.
If the user uses another DBMS you just change the datasource in app.php, and make the views if it's necessary
If the data is distributed in different DBMS, CakePHP let's you set a datasource for each table, you just add it to app.php and call it in the table if it's required.
Finally, in case you just need the "reading" option, create a user with limited access to the views and only with SELECT privileges.
USING:
CakePHP 3.2
SQL SERVER 2016
MySQL5.7

Grails: Best approach to dealing with an existing database

I'm writing a Grails application that will be pulling data from an existing Oracle database. If I were designing this from scratch I could hold all the information in two or three domain models because logically that's how the data should be arranged. However, this is a pre-existing database that has the data I need spread across approximately 25-30 tables. So I am wondering which of the following approaches would be considered best. I don't want to do tons of extra work to take advantage of what Grails has to offer, but at the same time I'd like to take advantage of as much of Grails as possible.
Create domain models for all 25-30 tables and then gather the data into two or three classes.
Create the two or three domain models and populate them "manually" with SQL calls
Since I'm new to Grails and how it handles data, something else that I haven't thought of yet.
There is one answer to all of your queries:
database-reverse-engineer plugin
You can configure the way you want to reverse engineer the tables to domain classes. Refer docs as well.

Use a lot of stored procedures from C#

I'm looking at a project where the customer has a legacy database (MS SQL) with a lot of sps (around 250). I need to be able to talk to all of these from my C# project but trying to find a good way to generate as much of the plumbing as possible.
I'm not sure if I should go with an ORM or some code generation tool? Pros and cons? I've looked at entity framework and it's ability to use complex types as strongly typed models but I would rather have a poco model and populate my objects in some way. It seems that miniORMs like ie. PetaPoco could be the way to go?
Anyone that has any tips and thoughts to share on this issue?
You'll need an ORM that does Reverse Stored-Procedure Mapping, like Telerik's OpenAccess ORM.
Telerik OpenAccess ORM provides the ability to import and use stored
procedures already existing in the database. They can be mapped to
static methods or used internally to replace the default write
operations and implement custom logic.
Telerik OpenAccess is now free. I guess they realized they couldn't sell an ORM when there are so many free alternatives like nHibernate available.
If you're looking for a lightweight alternative that can map stored procedures, try Sam Saffron's Dapper. Dapper is what drives Stack Overflow.
https://stackoverflow.com/a/6645870
http://code.google.com/p/dapper-dot-net/
PetaPoco works well with stored procs.
I'm if you wanted to you could write a Stored Proc mapper with a T4 template.
The template that you get with PetaPoco doesn't (at least last time I looked) map stored procs.
You could probably edit the template used here :
http://erraticdev.blogspot.co.uk/2010/11/t4-template-to-generate-bltoolkit.html
http://code.google.com/p/bltoolkit-storedprocedures2csharp-t4/
Just seen your comment about the way petapoco stored procs are called, thats true... I have only ever used it with MSSQL so possibly an over site from my there.

Retrieve data from a SQL Server stored procedure into a List<T>

I have this project that I am creating a library to handle all the data from multiple projects, I have organized the queries in stored procedures. I need to pass 4 parameters to the store procedure and get back some data. I cannot believe there is no easy way to accomplish this.
I have tried the datareader, datatable I do not want to have to iterate through the data as it does have the possibility to grow large.
Thank you for your help.
I would suggest using Dapper http://code.google.com/p/dapper-dot-net/
It's a micro ORM, much faster than EF - written by and used by guys behind SO ;-)
Note: I do not want to have to iterate through the data as it does have the possibility to grow large - someone will have to iterate through the result set - either you or the framework you will be using. Consider paging if you think you might get too much data at once.
Entity Framework is nice.
Add new item > ADO.NET entity Model
Generate from database
select only the SP's, unless you want to import the table schema too.
Once it finds your SP's, it will create complex types for you and everything will be really easy.
entity Framework for the win.

Is there a database like this?

Background: Okay, so I'm looking for what I guess is an object database. However, the (admittedly few) object databases that I've looked at have been simple persistence layers, and not full-blown DBMSs. I don't know if what I'm looking for is even considered an object database, so really any help in pointing me in the right direction would be very appreciated.
I don't want to give you two pages describing what I'm looking for so I'll use an example to illustrate my point. Let's say I have a "BlogPost" object that I need to store. Something like this, in pseudocode:
class BlogPost
title:String
body:String
author:User
tags:List<String>
comments:List<Comment>
(Assume Comment is its own class.)
Now, in a relational database, author would be stored as a foreign key pointing to a User.id, and the tags and comments would be stored as one-to-many or many-to-many relationships using a separate table to store the relationships. What I'd like is a database engine that does the following:
Stores related objects (author, tags, etc.) with a direct reference instead of using foreign keys, which require an additional lookup; in other words, objects on top of each other should be natively supported by the database
Allows me to add a comment or a tag to the blog post without retrieving the entire object, updating it, and then putting it back into the database (like a document-oriented database -- CouchDB being an example)
I guess what I'm looking for is a navigational database, but I don't know. Is there anything even remotely similar to what I'm thinking of? If so, what is it called? (Or better yet, give me an actual working database.) Or am I being too picky?
Edit:
Just to clarify, I am NOT looking for an ORM or an abstraction layer or anything like that. I am looking for an actual database that does this internally. Sorry if I'm being difficult, but I've searched and I couldn't find anything.
Edit:
Also, something for the JVM would be excellent, but at this point I really don't care what platform it runs on.
I think what you are describing could easily be modeled in a graph database. Then you get the benefit of navigating to the nodes/edges where you want to make changes without any need to retrieve anything else. For the JVM there's the Neo4j open source graph database (where I'm part of the team). You can read about it over at High Scalability, as part of an overview at thinkvitamin or in this stackoverflow thread. As for the tags, I think storing them in a graph database can give you some extra advantages if you want to find related tags and similar stuff. Just drop a line on the mailing list, and I'm sure the community will help you out.
You could try out db4o which is available in C# and Java.
I think our looking for this: http://www.odbms.org/. This site has some good info on Object Databases, including Objectivity, which is a pretty good object database.
Elephant does this: http://common-lisp.net/project/elephant/
Exactly what you've described can be done with (N)Hibernate running on an ordinary RDBMS.
The advantage of using such a persistence layer with an ordinary database is that you have a standard database system combined with convenient programming. You declare your classes in a very natural way, and (N)Hibernate provides a way to translate betweeen references/lists and foreign key relationships.
Java tutorial: http://docs.jboss.org/hibernate/stable/core/reference/en/html/tutorial-firstapp.html
.NET tutorial: https://web.archive.org/web/20081212181310/http://blogs.hibernatingrhinos.com/nhibernate/archive/2008/04/01/your-first-nhibernate-based-application.aspx
If you insist that you don't want to use a well-supported standard RDBMS and would rather trust your data to something more exotic and less heavily tested, you're looking for an Object Relational Database.
However, such a product would probably be best implemented by making it be a layer over a standard RDBMS anyway. This is probably why ORMs like (N)Hibernate are the most popular solution - they allow standard RDBMS software (and widely available management/user skills) to be applied, and yet the programming experience is 99% object-based.
This is exactly what LINQ was designed for.
Microsoft LINQ defines a set of proprietary query operators that can be used to query, project and filter data in arrays, enumerable classes, XML (XLINQ), relational database, and third party data sources. While it allows any data source to be queried, it requires that the data be encapsulated as objects. So, if the data source does not natively store data as objects, the data must be mapped to the object domain. Queries written using the query operators are executed either by the LINQ query processing engine or, via an extension mechanism, handed over to LINQ providers which either implement a separate query processing engine or translate to a different format to be executed on a separate data store (such as on a database server as SQL queries (DLINQ)). The results of a query are returned as a collection of in-memory objects that can be enumerated using a standard iterator function such as C#'s foreach.
There's a variety of terms, all linked to Object-Relational Mapping, aka ORM, which is probably going to be the most useful one for you to look up. ORM libraries exist for many programming languages.
Oracle's nested tables provide some part of that functionality, though in updates, you cannot just add a row to the nested table - you have to replace the whole nested table.
I guess you're looking for an ORM with "EntityFirst" approach.
In EntityFirst approach the developer is least[not-at-all] concerned with Database. You just have to build your entities or objects. The ORM then takes care of storing the entities in Database and retrieving them at your will.
The only EntityFirst ORM witihn my knowledge "Signum". It's a wonderful framework built on top of .net. I recommend you to go thrgouh some videos on the SignumFramework website and I'm sure you'll find it useful.
Link Text: http://www.signumframework.com
Thanks.
ZODB perhaps?
good introduction find here:
http://www.ibm.com/developerworks/aix/library/au-zodb/
You could try out STSdb, DB4O, Perst ... which is available in C# and Java.

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