I'm using EF 6 to query my database. I have a structure when I have a table (sites) which has 4 associated tables (wages, waste, sales & availability) linked by site ID.
The sub tables then all have an association to a departments table.
I have disabled lazy loading for performance reasons. I was wondering if there is a way to query the sites table where I can include the 4 sub tables but not need to specify the include to the department table for each of these.
Thanks
Turns out that simply adding an include to departments from one of the four tables (wages etc) was sufficent.
Related
In my database I have
a Members table which contains basic member details (MemberId [primary key - auto generated number], MemberName, IsActive).
a MembersDetails table which contains more detailed information about the member (Address, Phone, Birthday ...). MembersDetails has MemberId field as a foreign key to the Members table.
There's a reason (part of the app logic) that the 2 tables are separated and are not all in one table.
I've created a view that gets a full member details (a join of the 2 tables), and Entity Framework created an object that represents the view.
I have 2 questions:
Is there a better way of flattening 2 joined tables into an object other than creating a view in the database?
I would like to create an object of the view type (a full user details), initialize it's properties and insert it to the database (which will put the info it needs in the Members table, the the generated id, and than insert to the MemberDetails table). Is there a way to do that?
Ad 1.
I think a database view will be a good choice for performance reasons.
But you can investigate an inheritance provided with the Entity Framework.
It allows you join two separated tables in one model object containing all properties (from "derived" and "base" table). Note, it will be OK for one to one relations (but not for one to many).
Implementing Inheritance with the Entity Framework 6 in an ASP.NET MVC 5 Application
Ad 2.
The Entity Framework inheritance will help you with this issue well. Alternatively, if you can use a database view, just create stored procedures for inserting and updating data included in a view, then map the stored procedures for specified actions on the view model generated by Entity Framework.
I am using EF 6 Code-First, table per type, and I have two concrete classes Group and User. Group has a navigation property Members which contains a collection of User. I have mapped this many-to-many relationship in EF using Fluent syntax:
modelBuilder.Entity<Group>
.HasMany<User>(g => g.Members)
.WithMany(u => u.Groups);
I would like to be able to say when a member has joined a group so that I can query for, say, the newest member(s). I am not sure of how this is best accomplished within the framework.
I see the following options:
Create and use an audit table (ie GroupMembershipAudit consisting of Group, User, join/unjoin, and DateTime
Add a column to the autogenerated many-to-many table between User and Group
Is there anything within EF to facilitate this sort of storage of many-to-many historical info like this / append columns to the many-to-many relationship?
Add a column to the autogenerated many-to-many table between User and
Group
That is not possible - auto-generated junction tables can contain only keys (that is called Pure Join Table). According to Working with Many-to-Many Data Relationships article: If the join table contains fields that are not keys, the table is not a PJT and therefore Entity Framework cannot create a direct-navigation (many-to-many) association between the tables. (Join tables with non-key fields are also known as join tables with payload.)
Create and use an audit table (ie GroupMembershipAudit consisting of
Group, User, join/unjoin, and DateTime
Actually you should create GroupMembershipAudit entity. With Code First table will be generated, you don't need to create it manually.
I'm really new to Entity Framework (currently using EF5) and vs2012 and am having difficulty trying to figure something out.
I have an .edmx that was generated from my database. It has two tables in it: Item and 3rdPartyItem. In short, the Item table is the main table for all the company items while the 3rdPartyItem table is a table that is used to hold additional attributes for items. This 3rdPartyItem table was created by an outside company and is used with their software for the company, so I can't mess with either table. What I'm trying to do is show a list of Items in a grid but I need to show a combination of all the fields for both tables. In vs2012, if I create a relationship and make it 'zero-to-one' (because for each record in the Item table, there doesn't necessarily have to be one in the 3rdPartyItem table), vs complains about not being mapped correctly. When I set the mapping, it then complains that there's multiple relationships. I did some research and found that you can't create a relationship with 2 primary keys, so I was thinking that was the problem. But how can I change the .edmx so that in code, I can access Items and 3rdPartyItem like so:
var items = dbContext.Items;
items.3rdPartyItem.SomeField <--field from 3rdPartyItem table.
not too sure if it's even possible, but it would be very, very helpful if so. Any ideas?
What you're looking for is table-per-type (TPT) mapping inheritance. You can view an MSDN walkthrough here (although you'd want your base type to be instantiable):
http://msdn.microsoft.com/en-us/data/jj618293.aspx
In our shop, when we design a database, we typically include auditing attributes for each table (LastUpdateUser, LastUpdateDate, etc). This is common practice, however, I've noticed this becoming an increasing problem when you have tables that "inherit" from other tables, especially using tools such as the entity framework.
For example, if you have tables Customers and Employees, and those tables have a foreign key to table People, then in your entity / class model when you establish the inheritance, you need to change the names for the audit fields because they exist in both tables. Perhaps they need to become PersonLastUpdatedUser and PersonLastUpdatedDate, while the ones from Employees remain as simply LastUpdatedUser and LastUpdatedDate.
When designing tables for inheritance, do you put such audit fields in both tables, or do you just have them in the parent table and update the parent table whenever an attribute changes in a child table?
If you want to use inheritance than those attributes belong to parent table because the parent with related table forms single entity and you track auditing for whole entity. If you for any reason needs those attributes in both tables it should be the first warning that those tables are not good candidates for inheritance.
If you want true auditing, you create separate audit tables that are populated by triggers (never ever by the application or you will miss items that need to be audited).
and they shouw both the old and new value as well as the date and the user or application that made the change.
If you want a last updatedcolumn in each table (which I think is better than having it only in the parenta as that doesn't tell you anything about which of the tables changes last) and you want o use inheritance then you might need to create unique names by adding the table name to lastUpdated. So PersonLastUpdated and OrderLastUpdated, etc.
Or you don't use inheritance.
I'm using Eclipselink to map my tables to entities.
I have one big database table (actually it's view) with columns like groupId, groupName, categoryId, categoryName etc. I know it's redundand, but we're trying to minimize queries and it's dynamically created view.
The question is: How to map such table to several entities like Group, Category etc?
You would probably be better off mapping to the real tables and use query optimization to reduce your queries (such as join fetching and batch fetching)
See,
http://java-persistence-performance.blogspot.com/2010/08/batch-fetching-optimizing-object-graph.html
If you really want to have several class map to the same table, you will need to have one Entity and make the rest Embeddables.
See,
http://en.wikibooks.org/wiki/Java_Persistence/Embeddables