After reading the excellent article about entity framework on Postgresql by Brice Lambson, I decided to write this post to document my experience playing with Entity Framework 4.3.1 and Npgsql. This post will be an adaptation of the Code First To a New Database walkthrough in order to make it work with Npgsql.
You should follow the first 4 steps of Code First To a New Database. Go ahead, I''l wait for you.
Next stepsHere is where the adaptation of the walkthrough begins. As Brice noted in his post, Npgsql currently doesn't support database creation. ( I'm working on that and hope to get news about it soon.) So, for while, you have to create the database manually.
Those are the steps you have to do to create the database and the model:
> createdb ef_code_first_sample
create table "Blog" ("BlogId" serial, "Name" varchar(255));
create table "Post" ("PostId" serial, "Title" varchar(255), "Content" varchar(8000), "BlogId" int);
And here comes the first trick you have to use when working with EF and Npgsql: the table names as well as column names need to be double quoted.
Entity Framework generates code with table and column names double quoted and, to Postgresql, using double quotes means you want to preserve the casing of the names. So you need to create the tables with the correct case or else, Postgresql will complain it can't find your tables.
With the database and tables created, let's make some more configuration before we can run the sample.
Entity Framework installation
Unfortunately Npgsql doesn't support EF 5. Currently it supports 4.3.1 and there is a pull request by Pēteris Ņikiforovs to add support for EF 6. Yeah, Npgsql will have support for latest EF version soon!
You will need to install the 4.3.1 version of EF. According to EF Nuget project page, this is done with the following command:
PM> Install-Package EntityFramework -Version 4.3.1
This is needed because if you don't specify the 4.3.1 version, Nuget will install the latest version which isn't supported by Npgsql yet.
If you don't have Npgsql installed already, you should install Npgsql from Nuget too:
PM> Install-Package Npgsql
And then you should configure Npgsql in your App.config to be found by the DbProviderFactory API:
<add name="Npgsql Data Provider"
description="Data Provider for PostgreSQL"
type="Npgsql.NpgsqlFactory, Npgsql" />
and configure your connection string in the same App.config file:
Running the code
Now it's time to run the code. If you have everything configured and hit Ctrl+F5 you should get the code running and will be greeted with the Blog name question.
Unfortunately after answering the question and pressing enter, an exception will be thrown:
Unhandled Exception: System.Data.Entity.Infrastructure.DbUpdateException: An error occurred while updating the entries. See the inner exception for details. ---
> System.Data.UpdateException: An error occurred while updating the entries. See the inner exception for details. ---> Npgsql.NpgsqlException: ERROR: 3F000: schema "dbo" does not exist
This error occurs because by default, Entity Framework uses the schema dbo and Postgresql uses the schema public. This is the message you get in the Postgresql log:
INSERT INTO "dbo"."Blogs"("Name") VALUES (E'test');SELECT currval(pg_get_serial_sequence('"dbo"."Blogs"', 'BlogId')) AS "BlogId"
ERROR: schema "dbo" does not exist at character 13
As pointed out by Brice in his answer to a user question about this error, you have to tell Entity Framework to use a different schema. This is done by using Data Annotations and adding a Table attribute to the classes of the model:
public class Blog
[Table("Post", Schema = "public")]
public class Post
LOG: statement: INSERT INTO "public"."Blog"("Name") VALUES (E'test');SELECT currval(pg_get_serial_sequence('"public"."Blog"', 'BlogId')) AS "BlogId"
To use those attributes, you have to import the Data Annotations namespace:
More information about that can be found in the Code First To a New Database article linked at the beginning of this post.
That's it! After making those changes, you should now get the data correctly inserted in the database and everything should work ok:
I hope you enjoyed this post and could get started to Entity Framework and Npgsql. Please, let me know what you think in your comments.
I'd like to thank Brice Lambson for his excellent article and the Microsoft Entity Framework team for their Code First To a New Database walkthrough and all the EF stuff.