CODEWITHSUNDEEP
entity-frameworkdatabase-designef-code-first
Cyril Mestrom
Cyril Mestrom

Reputation: 6212

Setting up relation to base model which has many classes that inheritate in Code First Entity Framework

I'm creating my db using code-first and entity framework. I'm defining all my models which works great, but now I have a Page class which can contain Blocks. These Blocks have a base class with ID, BlockType, Position, Name etcetera but there are different types of blocks with different properties which are classes that inherit from this base class. I'm wondering how I can setup my models so the page can have a collection of 'blocks' without storing the custom properties in a comma seperated list or something like that. Is it possible? And what is the 'good' way to model this..

Thanks in advance!

Upvotes: 0

Views: 226

Answers (1)

Slauma
Slauma

Reputation: 177133

Entity Framework supports inheritance. There are various strategies to map your object model - base and derived classes - to a database schema. The most important are:

  • Table per hierarchy (TPH): Base class and all derived classes will be mapped to a single table in the database. Any custom properties of derived classes will appear as separate columns in the table and the table contains a discriminator column to distinguish between the types. EF manages to load the columns needed to materialize a specific type.

  • Table per type (TPT): The base class has its own table which only contains the base class properties. Every derived entity gets another table that has the additional properties of this type. EF manages to load the properties from the different tables (creating appropriate joins) that contain all properties to materialize a specific type.

TPT is - in my opinion - the cleaner approach to implement inheritance, but it currently (EF <= 4.3) has performance problems compared to TPH due to suboptimal SQL generated by EF. The problem will be solved in EF 5.0. But TPH will still remain the more performant way of mapping because it doesn't need to join multiple tables.

Benefits and drawbacks of the strategies are discussed in detail in the linked blog posts. In the blog you can also find the third (less often used) option - Table per concrete type (TPC).

Upvotes: 1

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