Changes for page The EOModel

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	3	+Work in progress! Right now, most of the text is coming from Apple's documentation. We need to change that, and add Wonder and WOLips specific information.
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3	3	= The EOModel =
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25	25	■ define derived attributes
26	26	■ build database queries in raw SQL
27	27
28		-In an Entity-Relationship model, distinguishable things are known as entities, each entity is defined by its component attributes, and the affiliations, or relationships between entities, are identified (together, attributes and relationships are known as properties). From these three simple modeling objects~-~--entities, attributes, and relationships~-~--arbitrarily complex systems can be modeled.
	34	+In an Entity-Relationship model, distinguishable things are known as entities, each entity is defined by its component attributes, and the affiliations, or relationships between entities, are identified (together, attributes and relationships are known as properties). From these three simple modeling objects~-~-entities, attributes, and relationships~-~-arbitrarily complex systems can be modeled.
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30	30	== Entities ==
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66	66
67	67	=== Advanced Entity Inspector ===
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69		-Batch Faulting Size lets you specify the number of faults that should be triggered when you first access an object of this type that is the destination of a to-many relationship. By providing a number in this field, you specify that number of faults of the same entity should be fetched from the data source along with the first fault. This improves performance by minimizing round trips to the data source.
	75	+**Batch Faulting Size** lets you specify the number of faults that should be triggered when you first access an object of this type that is the destination of a to-many relationship. By providing a number in this field, you specify that number of faults of the same entity should be fetched from the data source along with the first fault. This improves performance by minimizing round trips to the data source.
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71		-External Query lets you specify any SQL statement to execute when Enterprise Objects performs an unqualified fetch on the entity. The columns selected by this SQL statement must be in alphabetical order by internal name and must match in number and type with the class properties specified for the entity.
	77	+**External Query** lets you specify any SQL statement to execute when Enterprise Objects performs an unqualified fetch on the entity. The columns selected by this SQL statement must be in alphabetical order by internal name and must match in number and type with the class properties specified for the entity.
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73		-Qualifier is used to specify a restricting qualifier. A restricting qualifier maps an entity to a subset of rows in a table. When you add a restricting qualifier to an entity, it invokes a fetch for that entity to retrieve objects only of the type specified by the restricting qualifier. See "Implementing Single-Table Mapping in a Model" (page 77) for more information on restricting qualifiers.
	79	+**Qualifier** is used to specify a restricting qualifier. A restricting qualifier maps an entity to a subset of rows in a table. When you add a restricting qualifier to an entity, it invokes a fetch for that entity to retrieve objects only of the type specified by the restricting qualifier. See "Implementing Single-Table Mapping in a Model" (page 77) for more information on restricting qualifiers.
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75		-Parent is used to specify a parent entity for the current entity. This field is used to model inheritance. See "Modeling Inheritance" (page 67) for more details on this topic.
	81	+**Parent** is used to specify a parent entity for the current entity. This field is used to model inheritance. See "Modeling Inheritance" (page 67) for more details on this topic.
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77		-Read Only specifies whether the data that's represented by the entity can be altered by your application. This does not lock objects at the database level but rather works at a higher level (in the com.webobjects.eoaccess.EODatabaseContext object) so that if you try to save changes to data that's marked as read only, Enterprise Objects refuses the save and throws an exception.
	83	+**Read Only** specifies whether the data that's represented by the entity can be altered by your application. This does not lock objects at the database level but rather works at a higher level (in the com.webobjects.eoaccess.EODatabaseContext object) so that if you try to save changes to data that's marked as read only, Enterprise Objects refuses the save and throws an exception.
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79		-Cache in Memory specifies that when one record in a table is fetched, the entire table is fetched into memory. Caching an entity's objects allows Enterprise Objects to evaluate queries in memory, thereby avoiding round trips to the data source. This is most useful for read-only entities where there is no danger of the cached data getting out of sync with the data in the data source.
	85	+**Cache in Memory** specifies that when one record in a table is fetched, the entire table is fetched into memory. Caching an entity's objects allows Enterprise Objects to evaluate queries in memory, thereby avoiding round trips to the data source. This is most useful for read-only entities where there is no danger of the cached data getting out of sync with the data in the data source.
80	80
81		-Abstract lets you specify whether the entity is abstract. An abstract entity is one for which no objects are ever instantiated. For example, in the Real Estate database, the User entity is abstract and is never instantiated, whereas entities that inherit from it, such as Agent and Customer, are concrete classes that are instantiated. Like the Parent field, this option is used when modeling inheritance.
	87	+**Abstract** lets you specify whether the entity is abstract. An abstract entity is one for which no objects are ever instantiated. For example, in the Real Estate database, the User entity is abstract and is never instantiated, whereas entities that inherit from it, such as Agent and Customer, are concrete classes that are instantiated. Like the Parent field, this option is used when modeling inheritance.
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83	83	== Attributes ==
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114	114	~1. An entity named EOAdaptorNamePrototypes, where AdaptorName is the name of the adaptor for your model. WebObjects 5.2 includes an adaptor for JDBC data sources and an adaptor for JNDI data sources. So you can create a prototype entity called either EOJDBCPrototypes or EOJNDIPrototypes, depending on the adaptor you use.
115	115	2. An entity named EOPrototypes.
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117		-To create a prototype attribute, first create a prototype entity~-~--an entity named either EOAdaptorNamePrototypes or EOPrototypes~-~--and add an attribute to it. Figure 3-3 shows an attribute in a prototype entity. It shows all the values that prototype attributes can define: column name, value class, external type, and value type.
	123	+To create a prototype attribute, first create a prototype entity~-~-an entity named either EOAdaptorNamePrototypes or EOPrototypes~-~-and add an attribute to it. Figure 3-3 shows an attribute in a prototype entity. It shows all the values that prototype attributes can define: column name, value class, external type, and value type.
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119	119	To assign a prototype attribute to an attribute, reveal the Prototype column in table mode, and select a prototype attribute from the pop-up menu. The prototype attributes that appear in the pop-up list in the Prototype column include prototype attributes defined in any entity in any model in the application's model group, which includes the current model.
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184	184	==== Delete Rule ====
185	185
186	186	The options in the Delete Rule section specify what to do when the source object of a relationship is deleted. There are four options:
187		-■ Nullify disassociates all destination objects from the source object by removing references to them. So, when an Agent object is deleted, its related Customer objects are not deleted but the Customer objects' references to Agent are nullified (the entry in the join table is set to null).
188		-■ Cascade deletes all objects that are the destination of a relationship whose source is deleted. So, when an Agent object is deleted, all of its related Customer objects are also deleted.
189		-■ Deny refuses the deletion if a source object has any destination objects. So, if an Agent object has any Customer objects, deleting the Agent object is denied. In order for the deletion of the Agent object to succeed, its destination objects (Customer objects) must either be deleted or changed to something other than destination objects of the Agent object.
190		-■ No Action deletes the destination object but does not remove any back references to the source object. So, if a Customer object is deleted, its reference to its Agent object is not removed. Using this option may result in dangling references in the data source.
	193	+■ **Nullify** disassociates all destination objects from the source object by removing references to them. So, when an Agent object is deleted, its related Customer objects are not deleted but the Customer objects' references to Agent are nullified (the entry in the join table is set to null).
	194	+■ **Cascade** deletes all objects that are the destination of a relationship whose source is deleted. So, when an Agent object is deleted, all of its related Customer objects are also deleted.
	195	+■ **Deny** refuses the deletion if a source object has any destination objects. So, if an Agent object has any Customer objects, deleting the Agent object is denied. In order for the deletion of the Agent object to succeed, its destination objects (Customer objects) must either be deleted or changed to something other than destination objects of the Agent object.
	196	+■ **No Action** deletes the destination object but does not remove any back references to the source object. So, if a Customer object is deleted, its reference to its Agent object is not removed. Using this option may result in dangling references in the data source.
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192	192	=== Tips ===
193	193
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242	242	You can set up an EOModel so that Enterprise Objects automatically invokes a stored procedure for these operations on an entity:
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244		-Insert to insert a new object into an entity
245		-Delete to delete an object from an entity
246		-Fetch All to fetch all objects in an entity
247		-Fetch w/ PKto fetch the object in an entity with a particular primary key
248		-Get PK to generate a new primary key for an entity
	250	+**Insert** to insert a new object into an entity
	251	+**Delete** to delete an object from an entity
	252	+**Fetch All** to fetch all objects in an entity
	253	+**Fetch w/ PK** to fetch the object in an entity with a particular primary key
	254	+**Get PK** to generate a new primary key for an entity
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250	250	The stored procedures you enter in the Stored Procedure Inspector must correspond to a stored procedure in the model. If you created the model from an existing data source and chose the Ask About Stored Procedures option in the wizard, stored procedures are already added to the model. If this is not the case, however, you can add stored procedures to the model using the Add Stored Procedure command from the Property menu.
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256	256	For each of the operations, if the stored procedure associated with an operation returns a value, Enterprise Objects ignores the return value.
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258		-For Fetch All operations, the stored procedure must not take any arguments and it should return a result set for all the objects in the corresponding entity. The rows in the result set must contain values for all the columns Enterprise Objects would fetch if it were not using the stored procedure, and it must return them in alphabetical order.
	264	+For **Fetch All** operations, the stored procedure must not take any arguments and it should return a result set for all the objects in the corresponding entity. The rows in the result set must contain values for all the columns Enterprise Objects would fetch if it were not using the stored procedure, and it must return them in alphabetical order.
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260	260	That is, the stored procedure should return values for primary keys, foreign keys used in class property joins, class properties, and attributes used for locking. These values must be returned in alphabetical order with regard to the attributes with which they are associated. For example, consider a Listing entity that has the attributes listingID, bedrooms, and sellingPrice. A stored procedure that fetches all the Listing objects should return the value for a listing's number of bedrooms, then its listingID, and then its selling price.
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262		-For Fetch w/ PK operations, the stored procedure must take an "in" argument for each of the entity's primary key attributes (most entities have a single primary key attribute). The argument names must match the names of the entity's primary key attributes. For example, a Listing entity has a single primary key attribute named listingID, so the stored procedures argument as defined in the model must also be listingID.
	268	+For **Fetch w/ PK** operations, the stored procedure must take an "in" argument for each of the entity's primary key attributes (most entities have a single primary key attribute). The argument names must match the names of the entity's primary key attributes. For example, a Listing entity has a single primary key attribute named listingID, so the stored procedures argument as defined in the model must also be listingID.
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264		-A Fetch w/ PK operation stored procedure should return a result set containing the row that matches the primary key passed in by the argument. The row must be in the same form as rows returned by the Fetch All operation.
	270	+A **Fetch w/ PK** operation stored procedure should return a result set containing the row that matches the primary key passed in by the argument. The row must be in the same form as rows returned by the Fetch All operation.
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266		-For Insert operations, the stored procedure must take an "in" argument for each of the corresponding entity's attributes. The argument names must match the names of the corresponding EOAttribute objects.
	272	+For **Insert** operations, the stored procedure must take an "in" argument for each of the corresponding entity's attributes. The argument names must match the names of the corresponding EOAttribute objects.
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268		-For Delete operations, the stored procedure must take an "in" argument for each of the entity's primary key attributes. The argument names must match the names of the primary key attributes as in a Fetch w/ PK operation stored procedure.
	274	+For **Delete** operations, the stored procedure must take an "in" argument for each of the entity's primary key attributes. The argument names must match the names of the primary key attributes as in a Fetch w/ PK operation stored procedure.
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270		-For Get PK operations, the stored procedure must take an "out" argument for each of the entity's primary key attributes. The argument names must match the names of the primary key attributes as in a Fetch w/ PK operation stored procedure.
	276	+For **Get PK** operations, the stored procedure must take an "out" argument for each of the entity's primary key attributes. The argument names must match the names of the primary key attributes as in a Fetch w/ PK operation stored procedure.
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272		-Insert, Delete, and Get PK operations should not return a result set.
	278	+**Insert**, **Delete**, and **Get PK** operations should not return a result set.
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274	274	== EO Inheritance ==
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276		-One of the issues that may arise in designing your enterprise objects~-~--whether you're creating a schema from scratch or working with an existing database schema~-~--is the modeling of inheritance relationships.
	282	+One of the issues that may arise in designing your enterprise objects~-~-whether you're creating a schema from scratch or working with an existing database schema~-~-is the modeling of inheritance relationships.
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278	278	In object-oriented programming, it's natural to think of data in terms of inheritance. A Customer object, for example, naturally inherits certain characteristics from a Person object, such as name, address, and phone number. In inheritance hierarchies, the parent object or superclass is usually rather generic so that less generic subclasses of a related type can easily be added. So, in addition to the Customer object, a Client object also naturally derives from a Person object.
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336	336	Single-table mapping results in tables that have columns for all of the attributes of each entity in the inheritance hierarchy. It also results in many null row values. While these aren't really disadvantages, they may conflict with some database design philosophies.
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	344	+=== Using Inheritance in Entity Modeler ===
	345	+
	346	+To use Inheritance in your model, you first need to create your base entity. When done, right-click on the entity and select Subclass. A dialog will appear and will ask you to specify which kind of Inheritance you want to use, which entity is the parent and the name of the new (child) entity. When selecting Vertical or Single-Table Inheritance, you can also specify the qualifier (type = XX) in that dialog (you can do that part later too).
	347	+
338	338	== EOGenerator ==
339	339
340	340	== Handling Blob Data ==