Design entity model

Trysil > Design entity model opens the designer of the active project. The left panel lists the entities, the right panel the properties (columns) of the selected entity.

Nothing is written to disk until you click Save. Cancel discards every change made since the designer was opened.

Entities

Use the buttons above the entity list:

Button	Action
Add new entity	Creates an entity
Edit entity	Changes name, table and sequence (also with a double click)
Delete entity	Removes the entity, after confirmation

The entity dialog has three fields:

Field	Meaning	Generated as
Entity name	Name of the Delphi class, without the T prefix	TCustomer
Table name	Database table	[TTable('Customers')]
Sequence name	Sequence that generates the primary key	[TSequence('CustomersID')]

While you type, the Expert suggests the table name from the entity name and the sequence name from the table name, followed by ID. A suggestion follows the field it comes from until you change it by hand.

The dialog refuses empty fields, a table named like its own sequence, and names already used by another entity: two entities cannot share the entity name, the table name or the sequence name, and a table cannot have the name of another entity's sequence. Names are compared ignoring case.

Every new entity starts with two columns that cannot be edited, moved or deleted:

Property	Column	Type
ID	ID	Primary key, TTPrimaryKey
VersionID	VersionID	Version for optimistic locking, TTVersion

ID is always the first column, VersionID always the last.

Properties

Use the buttons above the property list:

Button	Shortcut	Action
Add new property		Asks the column type, then opens its dialog
Edit property	double click	Changes the selected property
Delete property		Removes the property, after confirmation
Move property up	Ctrl+Up	Moves the property one place up
Move property down	Ctrl+Down	Moves the property one place down

The order of the properties is the order of the fields in the generated class and of the columns in the CREATE TABLE.

When you add a property, the Expert asks what kind of column it is:

Column type	What it is
Data column	A value: text, number, date, and so on
Entity column	A reference to another entity (a foreign key), loaded lazily
Entity list column	The list of the entities that refer to this one (a detail list), loaded lazily

Data column

Field	Meaning
Property name	Name of the Delphi field and property
Column name	Database column; suggested from the property name
Data type	See the table below
Size	Maximum length, for String only, and mandatory for it
Required	The column is NOT NULL and the field gets [TRequired]
Allow empty	For a String that is not required: see below

Data type	Delphi type
String	String, with [TMaxLength(Size)]
Memo	String, unlimited text
Smallint	Smallint
Integer	Integer
LargeInteger	Int64
Double	Double
Currency	Currency
Boolean	Boolean
DateTime	TDateTime
Guid	TGuid
Blob	TBytes

A column that is not required is generated as TTNullable<T>, for example TTNullable<Integer>, so that it can hold NULL.

Allow empty is the exception for text. A String column that is not required but allows empty is generated as a plain String, and its database column gets DEFAULT '': the value is never NULL, at most an empty string.

Entity column

An entity column is a reference to another entity of the model, like the customer of an order.

Field	Meaning
Property name	Name of the property, for example Customer
Column name	Database column with the foreign key; suggested as the property name followed by ID, for example CustomerID
Entity type	The entity referred to
Required	The reference cannot be empty

It is generated as a TTLazy<T> field with a property of the entity type, so the related entity is loaded the first time you read it. In the database it is an integer column.

Entity list column

An entity list column is the other side of a reference: the rows of an order.

Field	Meaning
Property name	Name of the property, for example Details
Entity type	The entity of the list, for example OrderDetail
Column name	The column of that entity that refers to this one, for example OrderID

It is generated as a TTLazyList<T> field, with a read-only property of type TTList<T>. It has no column of its own in the database: the list is read through the column of the other entity, and the Expert adds an index on that column to the DDL script.

Tip

Create the entities first, then the reference columns: the entity type lists only entities that already exist. For an entity list column, the column name lists the Integer data columns of the chosen entity, so the column on the other side must already be there.

No entity column back to the master

In the detail entity, the column that refers to the master is a plain Integer data column, like OrderID in OrderDetail. Do not add to the detail an entity column that points back to the master: the unit of the master uses the unit of the detail for the list, the unit of the detail would use the unit of the master for the reference, and Delphi does not compile two units that use each other in their interface.

Relations

The Expert derives the [TRelation] attributes from the reference columns, so that Trysil checks related rows on delete:

• an entity column on Order that refers to Customer adds to TCustomer a relation on Orders.CustomerID, without cascade: a customer with orders cannot be deleted;
• an entity list column Details on Order adds to TOrder a relation on the table of OrderDetail and its column OrderID, with cascade: deleting an order deletes its rows.

The Expert does not generate foreign key constraints in the database.