I have a database called MembershipType which contains 2 fields.
I added a new field call 'Name'. I wanted to hard-code the data in to the database by using a SQL query.
I wanted to seed data into the column 'Name' which is the other column is already filled with. Is that possible or not?
Related
I know that it is possible using #SqlResultSetMapping but I want to select not whole entity from the database but some fields and then map i to my entity using one of the constructor which accept that fields. Is that possible to map result with #EntityResult for only a few #FieldResult? I was trying to do that and all the time I get error which said that there is not specify mapping for some fields which exist in that entity.
The disadvantage of #SqlResultSetMapping is that you have to select all the columns.
The alternate way of doing this manually iterate over the DB result and populate your objects.
Well, if you are using JPA 1.0 your only option (not considering the manual mapping, of course), is to use #SqlResultSetMapping and map the whole table columns. With JPA 2.1 you can add a javax.persistence.ConstructorResult (see docs here) to map only the needed columns.
My database looks like this: Database Diagram MSSMS
So everytime i'm adding a fish to the database, i want to add the fishes's continent, waterlagen and verbanden.
Tables Continenten, Waterlagen & Verbanden are already filled with objects from an array after creating the database.
Im using List Continenten; for example to store multiple continents.
So i tryed:
Vis nieuweVis = new Fish();
nieuweVis.Naam = "Molly";
foreach(Continent c in Continenten)
nieuweVis.Continenten.Add(c)
so in the table VisContinenten
i assume that EF will automaticly fill in the FishId and ContinentId wich are foreignkeys.
I want records in that table also to be unique so i add a unique key to both the columns in VisContinenten so that fish 1 on continent 1 won't appear twice in that table.
Error i get:
An error occurred while saving entities that do not expose foreign key
properties for their relationships
Additional information: Unable to update the EntitySet 'VisContinenten' because it has a DefiningQuery and no element exists in the element to support the current operation.
Help me pls :)
Thank you
I have an entity class with a column called 'CalculatedId'. This column is obtained from an SQL statement and the column does NOT exist in the database table.
If I run app I get an error telling me that the column does not exist. This error is due to the framework trying to map the column to a physical column.
Below is my mapping code:
modelBuilder
.Entity<Widgets>()
.Property(x => x.CalculatedId)
.HasComputedColumnSql("select top 1 Id from MyTable");
I thought that this would tell EF not to look for a physical column as it's generated.
The only way I can get rid of the error is if I do this:
modelBuilder
.Entity<Widgets>()
.Ignore(x => x.CalculatedId);
Problem there is that the column is totally ignored an not generated at all.
Can someone please connect the dots for me and clarify what needs to be done to make sure that the column is generated but EF does not look for it in the database.
NB: Has to be done in the fluent API, no data annotations.
I created POCO classes and then EF created the database tables for me when I tried to access the data. This worked without problem. I have now populated my tables with data. Not just seed data but real data.
Now I would like to add another column to a table. I assume the first thing I need to do is to add a field to the POCO class but what's next after that? I now have my database filled with data. On the SQL side I know how to add the column myself but do I have to do something with EF or will it automatically pick up that my column was added to the table and my field to the POCO class?
You can use Code First Migrations (http://msdn.microsoft.com/en-us/library/hh770484(v=vs.103).aspx). It can update your database automatically or not.
Using Entity Framework CodeFirst, how do I create a created datetime column that gets populated with the current timestamp everytime a record is inserted for that table, and a modified datetime column that has a timestamp generated evertime a row is updated? Rails does this by default and I was hoping the EF generated database would have this as well, but it doesn't. Is this something that can be done with data annotations? If so, how?
Thanks!
It is not supported in EF. EF will not create these columns for you automatically. You must do it yourselves by either:
Have Created and Modified properties in every entity where you want to maintain these values. You must also manually maintain these columns in your application (common approach is overriding SaveChanges and set values accordingly).
If you don't need these values mapped (you never expect to use them in your application and you are happy with the logic in the database) you can create custom database initializer which would execute your custom SQL to alter tables and add those columns, default constraints for Created columns and update triggers for Modified columns.