set identity and computed properties in entity framework without triggers

28/3/2014 Set Identity and Computed Properties in Entity Framework Without Triggers

http://blog.devart.com/set-identity-and-computed-properties-in-entity-framework-without-triggers.html 1/9

Set Identity and Computed Properties in EntityFramework Without Triggers

Posted by dotConnect Team on August 9th, 2011

This article deals with the following:

StoreGeneratedPattern

IdentityComputed

DefaultValue

InsertNullBehaviourExample

Conclusion

StoreGeneratedPattern

Entity Framework contains an excellent functionality of server-generated columns of the entity that is intendedfor defining the primary key values on the database side, concurrency check and so on. This is done by setting

StoreGeneratedPattern of columns of the EF-model storage part (SSDL) to either Identity or Computed.

Identity

In a number of databases (Microsoft SQL Server, MySQL, PostgreSQL, SQLite),

StoreGeneratedPattern.Identity of the columns primary key is defined by the EF-designer when a model is

created against the database and if these columns are made auto-increment in the database. Oracle does nothave any standard way of making a column auto-increment, thus, in the database, the users have to create a

sequence and the BEFORE INSERT trigger that defines the value of an auto-increment column based on the

sequence; when the model is created, the users have to set the value of StoreGeneratedPattern manually in the

model editor.

Computed

In most cases, supporting this functionality involves writing UPDATE-triggers in the database, which takes

time and requires knowledge of a specific programming language other than SQL, for example, PL/SQL in



Oracle.

DefaultValue

To facilitate and speed up the process of development as well as to increase its flexibility, we have provided

the users of our EF-providers for Oracle, MySQL, PostgreSQL and SQLite with a capability that, in simple

cases, obviates the need to write INSERT and UPDATE triggers and to set a default value for columns in the

database. This can also be useful when you need, if possible, to use existing objects rather than modify thedatabase. Now, you can assign values to columns by specifying database functions in the columns

DefaultValue attribute in the storage part of the EF model (SSDL).

If you use Entity Data Model Designer, you will need to edit the models XML using an XML editor. Bear in

mind that the DefaultValue standard attribute is checked by EF-validation and that is why it cannot be used to

call a DB-function. For that reason, we have introduced the new custom devart:DefaultValue SSDL attribute

(if you need to edit manually the EDMX file, do not forget to add the attribute

xmlns:devart=http://devart.com/schemas/edml/StorageSchemaExtensions/1.0 to the tag Schema in SSDL).The devart:DefaultValue attribute does not trigger the type consistency check, so you can use a wider range ofdefault values, like CURRENT_TIMESTAMP or MY_SEQUENCE.NEXTVAL.

If you use Devart Entity Developer, you will be able to set the value for DefaultValue in the designer, and it

will store this value correctly either in the DefaultValue attribute or in devart:DefaultValue , as required.

InsertNullBehaviour

To use this functionality, you need to configure the EF-provider. For more information on the specifics ofconfiguration, see New Features of Entity Framework Support in dotConnect Providers; for the purpose of

the present article we shall review a small example that shows how to customize the DefaultValue processingbehavior. In this example, we deal with the dotConnect for Oracle provider, but the procedure is identical forMySQL, PostgreSQL, and SQLite.

New features are configured in the EntityProviderConfig class. This class is available in theDevart.Data..Entity assembly. Dont forget to add this Devart.Data.

.Entity.dll assembly as Reference for the corresponding Entity Framework version (supportfor the new functionality is available for EF v1 and v4.x).For more information on capabilities of InsertNullBehaviour, see here.

Example

As an example, we shall use a table in Oracle, in which we want to define the behavior of the store generatedcolumns in the model rather than create triggers. For the purpose of this example, we also suppose that we

already have a sequence (MY_SEQUENCE) and a database function (MY_FUNCTION) that we can nowuse. Lets demonstrate all the capabilities within a single example.

var config = OracleEntityProviderConfig.Instance; config.DmlOptions.InsertNullBehaviour = InsertNullBehaviour.InsertDefaultOrNull;// orconfig.DmlOptions.InsertNullBehaviour = InsertNullBehaviour.InsertDefaultOrOmit;



Below is the script for creating the table:

XML-representation of the entity in the storage model (SSDL):

Now we shall modify mapping by defining the following rules:

The ID column, which is the primary key, will be defined through the value of the sequenceMY_SEQUENCE on INSERT.The FunctionGeneratedValue column will be defined through the call of the user-defined function

MY_FUNCTION() on INSERT.

The ModifiedBy will be defined through the system database function USER on INSERT andUPDATE.

The LastModified column will be defined through the system database function

CURRENT_TIMESTAMP on INSERT and UPDATE. This column will be used for concurrencycheck, so we need to set ConcurrencyMode=Fixed for this column in the conceptual model.

XML SSDL after modification is shown below:

CREATE TABLE "Products" ( ID NUMBER(9) PRIMARY KEY, "ProductName" VARCHAR2(160) NOT NULL, "Price" NUMBER(10, 2), "FunctionGeneratedValue" NUMBER NOT NULL, "ModifiedBy" VARCHAR2(30) NOT NULL, "LastModified" TIMESTAMP NOT NULL)



Below shown is an example of C# code:

To monitor queries sent to the server, we recommend that you use Devart dbMonitor, a free tool, that iscompatible with Devart EF-providers. However, the use of this monitor is recommended only on the stage of

development and debugging of the application, since its use causes a drop in performance.

Shown below is SQL generated on INSERT:

Shown below is SQL generated on UPDATE:

// Here we turn on the monitoring of interaction with the database through dbMonitorvar mon = new Devart.Data.Oracle.OracleMonitor { IsActive = true }; // Here we configure the EF-provider, so that the default values defined in the model are used var config = OracleEntityProviderConfig.Instance;config.DmlOptions.InsertNullBehaviour = InsertNullBehaviour.InsertDefaultOrNull; // Here we create the context and perform insert and update of the entity using (var ctx = new Entities()) { Products product = new Products() { ProductName = "Gadget", Price = 220.25 }; ctx.Products.AddObject(product); ctx.SaveChanges(); // INSERT product.Price = 199.99; ctx.SaveChanges(); // UPDATE}

DECLARE updatedRowid ROWID;BEGININSERT INTO "Products"(ID, "FunctionGeneratedValue", "ModifiedBy", VALUES (MY_SEQUENCE.NEXTVAL, MY_FUNCTION(), USER, CURRENT_TIMESTAMPRETURNING ROWID INTO updatedRowid;OPEN :outParameter FOR SELECT ID, "FunctionGeneratedValue", "ModifiedBy"END;

DECLARE updatedRowid ROWID;BEGINUPDATE "Products" SET "ModifiedBy" = USER, "LastModified" = CURRENT_TIMESTAMP, "Price" WHERE ID = :p1 AND "LastModified" = :p2RETURNING ROWID INTO updatedRowid;OPEN :outParameter FOR SELECT "ModifiedBy", "LastModified" FROM "Products"

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Conclusion

As we have seen, this functionality is extremely simple to use. If you, as yet, do not use Entity Developer,

whose EF-version is shipped with our EF-providers, consider doing so, since it allows modifying the storagemodel much more easily and more conveniently than a standard EDM designer does and hence is a more

suitable tool for this purpose. Nor should you forget to monitor SQL being sent on the development stage, so

that you can be sure that everything works as intended.

See also

Oracle 12c Support and More New Features in New Versions of Devart Products

Model-Defined Functions in Entity DeveloperEnhanced Entity Framework Spatials support for Oracle, MySQL and PostgreSQL

Entity Framework 6 Support for Oracle, MySQL, PostgreSQL, SQLite, DB2 and Salesforce

New Features in Entity Developer 5.0

2 Responses to Set Identity and Computed Properties in Entity FrameworkWithout Triggers

1. Max1ce Says: November 15th, 2011 at 5:30 pm

How would you use the DefaultValue in a code-first approach without using the designer?

2. Shalex Says: November 17th, 2011 at 1:25 pm

Microsoft does not allow setting default value in the current version of EF Code-First fluent mapping.

There are several suggestions about the default value support at official Entity Framework UserVoice:http://data.uservoice.com/forums/72025-ado-net-entity-framework-ef-feature-

suggestions/suggestions/1050341-allow-setting-default-values-from-model?ref=title

http://data.uservoice.com/forums/72025-ado-net-entity-framework-ef-feature-suggestions/suggestions/1501715-more-options-in-code-first-db-generation?ref=title

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