{"id":620,"date":"2009-09-21T21:49:11","date_gmt":"2009-09-21T20:49:11","guid":{"rendered":"http:\/\/www.gamlor.info\/wordpress\/?p=620"},"modified":"2021-03-11T09:44:58","modified_gmt":"2021-03-11T08:44:58","slug":"db4o-the-basics","status":"publish","type":"post","link":"https:\/\/www.gamlor.info\/wordpress\/2009\/09\/db4o-the-basics\/","title":{"rendered":"db4o, The Basics"},"content":{"rendered":"

With this post I start a little series about db4o<\/a>, an object database. Why? Because I think object databases are a quite unknown technology. Normally when developers talk about databases they mean a relational database. Yes, relational databases are awesome and well known. But there are lots of alternatives out there! Sadly, lots of developer never even look at alternatives. For example graph-databases like Neo4J<\/a>, document-database like CouchDB<\/a> or a object-database like db4o<\/a>.<\/p>\n

(All posts of this series: the basics<\/a>, activation<\/a>, object-identity<\/a>, transactions<\/a>, persistent classes<\/a>, single container concurrency<\/a>, Queries in Java, C# 2.0<\/a>, client-server concurrency<\/a>, transparent persistence<\/a>, adhoc query tools<\/a>)<\/p>\n

I will stick to the .NET 3.5 version of db4o. Although db4o supports different Java-, .NET and Mono-versions.<\/p>\n

The Database-Schema<\/h3>\n

<\/a><\/p>\n

\"db4o-plan\"<\/a><\/p>\n

In db4o your plain old C#-classes are actually the database-schema. So for our first steps we just use two object, people and pets:<\/p>\n

public<\/span> class<\/span> Pet\r\n{\r\n    public<\/span> Pet(string<\/span> name)\r\n    {\r\n        Name = name;\r\n    }\r\n\r\n    string<\/span> Name { get; set; }\r\n}<\/pre>\n
\u00a0<\/pre>\n
public<\/span> class<\/span> Person\r\n{\r\n    private<\/span> IEnumerable<Pet> _ownsPets;\r\n\r\n    public<\/span> string<\/span> FirstName { get; set; }\r\n    public<\/span> string<\/span> SirName { get; set; }\r\n    public<\/span> bool<\/span> IsMarried { get; set; }\r\n\r\n    public<\/span> IEnumerable<Pet> Owns\r\n    {\r\n        get { return<\/span> _ownsPets; }\r\n        set { _ownsPets = value<\/span>.ToArray(); }\r\n    }\r\n}<\/pre>\n
Store Some Objects<\/h3>\n
<\/a><\/p>\n
\"db4o-store\"<\/a><\/p>\n
Ok, this is a really simple task in db4o. Basically you create classes which represent your domain. Then you open a db4o-ObjectContainer and store them. Done!<\/p>\n
var config = Db4oEmbedded.NewConfiguration();\r\nusing<\/span> (var db = Db4oEmbedded.OpenFile(config, \"database.db4o\"<\/span>))\r\n{\r\n    var myself = new<\/span> Person\r\n                     {\r\n                         FirstName = \"Roman\"<\/span>,\r\n                         SirName = \"Stoffel\"<\/span>,\r\n                         Owns = new<\/span>[]\r\n                                    {\r\n                                        new<\/span> Pet(\"Findus\"<\/span>),\r\n                                        new<\/span> Pet(\"Garfield\"<\/span>),\r\n                                    }\r\n                     };\r\n    db.Store(myself);\r\n}<\/pre>\n
Get Objects Back<\/h3>\n
\"db4o-query\"<\/a><\/p>\n
Well storing was easy. But how do I get the objects back? Well what comes to mind immediately? LINQ! So queries are easy too!<\/p>\n
using<\/span> (var db = Db4oEmbedded.OpenFile(config, \"database.db4o\"<\/span>))\r\n{\r\n    var persons = from Person p in<\/span> db\r\n                  where<\/span> p.SirName.Contains(\"Stoffel\"<\/span>)\r\n                  select p;\r\n    foreach<\/span> (var aPerson in<\/span> persons)\r\n    {<\/pre>\n
        Console.Out.WriteLine(aPerson.FirstName);\r\n    }\r\n}<\/pre>\n
Update Objects<\/h3>\n
\"db4o-update\"<\/a><\/p>\n
Isn\u2019t that difficult as well.<\/p>\n
var config = Db4oEmbedded.NewConfiguration();\r\nusing<\/span> (var db = Db4oEmbedded.OpenFile(config, \"database.db4o\"<\/span>))\r\n{\r\n    var persons = from Person p in<\/span> db\r\n                  where<\/span> p.SirName.Contains(\"Stoffel\"<\/span>)\r\n                  select p;\r\n    foreach<\/span> (var aPerson in<\/span> persons)\r\n    {\r\n        aPerson.IsMarried = true<\/span>;\r\n        db.Store(aPerson);\r\n    }\r\n}<\/pre>\n
Deleting Objects<\/h3>\n
\"db4o-delete\"<\/a><\/p>\n
Ok, ok it\u2019s getting to boring:<\/p>\n
db.Delete(aPerson);<\/pre>\n
Next time<\/h3>\n
Well, this wasn\u2019t difficult so far. Next time I\u2019ll dive into a very important concept in db4o, the activation- and update-depth.<\/p>\n
\u00a0Example-Source-Code: Person.cs<\/a>\u00a0Pet.cs<\/a>\u00a0Program.cs<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"
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