i would like to know if you have any idea how i can achieve this, considering a query stored as string in the configuration file.
I tried to use SqlQuery applied to the DBSet, but the problem is that SqlQuery requires me to select all properties of the required entities in my query. If i don't consider any column, it will complain because is not able to map the query to the entities.
I don't want to select all properties of the entities i want to query.
Thanks
If you are using EF then why not use Database.ExecuteSqlCommand()? It's in the System.Data.Entity namespace.
For example:
int result = db.Database.ExecuteSqlCommand("Non SELECT SQL etc...");
Well, I ended up implementing a mechanism using reflection that basically receives a group of fields to select, and constructs dynamic objects with those fields, so when applied the query with the joins between the entities, will only bring the fields I am looking for.
So, considering Entity1, Entity2, Entity3 with the following relationship
<b>Entity1</b>{
<br/> Entity1Name, <br/> List<*Entity2*> Entity2Items, <br/> etc..
<br/>}
and
<b>Entity2</b> { <br/> Entity2Name, <br/> List<*Entity3*> Entity3Items <br/>}
I can store e.g. the following query in the configuration file, and retrieve the information:
"Entity1.Entity1Name", <br/>
"Entity1.Entity2Items.Entity2Name", <br/>
"Entity1.Entity2Items.Entity3Items.Entity3Name"
Anyway, I was just trying to see if there would be any solution out-of-the-box that would require minimal code changes.
Thank you.
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.
It is easy to do a Contains, StartsWith, or EndsWith query in Entity Framework when you know the pattern you'd like to find. But how to do the equivalent of "LIKE [Column]"?
For instance, this is easy:
Name LIKE '%Th'
But how do you do this? where Prefix is a column.
Name LIKE [Prefix]
I tried to use the SqlMethods and got the following error.
LINQ to Entities does not recognize the method 'Boolean Like(System.String, System.String)' method, and this method cannot be translated into a store expression.
I resolved this problem by using LINQ to Entities to bring back the set of data that I wanted, then using LINQ to Objects to filter the data.
I do not think there is currently a way to have a LINQ to Entities query be resolved in a database server as ...
... LIKE [column-name]
First, SqlMethods is for use in LINQ-to-SQL, not LINQ-to-Entities.
The best you can do to use the filter in the database engine (so you don't have to pull all data in memory first) is:
context.Entities.SqlQuery("SELECT * FROM EntityTable WHERE Name LIKE Prefix")
I have a legacy database with a particular table -- I will call it ItemTable -- that can have billions of rows of data. To overcome database restrictions, we have decided to split the table into "silos" whenever the number of rows reaches 100,000,000. So, ItemTable will exist, then a procedure will run in the middle of the night to check the number of rows. If numberOfRows is > 100,000,000 then silo1_ItemTable will be created. Any Items added to the database from now on will be added to silo1_ItemTable (until it grows to big, then silo2_ItemTable will exist...)
ItemTable and silo1_ItemTable can be mapped to the same Item entity because the table structures are identical, but I am not sure how to set this mapping up at runtime, or how to specify the table name for my queries. All inserts should be added to the latest siloX_ItemTable, and all Reads should be from a specified siloX_ItemTable.
I have a separate siloTracker table that will give me the table name to insert/read the data from, but I am not sure how I can use this with entity framework...
Thoughts?
You could try to use the Entity Inheritance to get this. So you have a base class which has all the fields mapped to ItemTable and then you have descendant classes that inherit from ItemTable entity and is mapped to the silo tables in the db. Every time you create a new silo you create a new entity mapped to that silo table.
[Table("ItemTable")]
public class Item
{
//All the fields in the table goes here
}
[Table("silo1_ItemTable")]
public class Silo1Item : Item
{
}
[Table("silo2_ItemTable")]
public class Silo2Item : Item
{
}
You can find more information on this here
Other option is to create a view that creates a union of all those table and map your entity to that view.
As mentioned in my comment, to solve this problem I am using the SQLQuery method that is exposed by DBSet. Since all my item tables have the exact same schema, I can use the SQLQuery to define my own query and I can pass in the name of the table to the query. Tested on my system and it is working well.
See this link for an explanation of running raw queries with entity framework:
EF raw query documentation
If anyone has a better way to solve my question, please leave a comment.
[UPDATE]
I agree that stored procedures are also a great option, but for some reason my management is very resistant to make any changes to our database. It is easier for me (and our customers) to put the sql in code and acknowledge the fact that there is raw sql. At least I can hide it from the other layers rather easily.
[/UPDATE]
Possible solution for this problem may be using context initialization with DbCompiledModel param:
var builder = new DbModelBuilder(DbModelBuilderVersion.V6_0);
builder.Configurations.Add(new EntityTypeConfiguration<EntityName>());
builder.Entity<EntityName>().ToTable("TableNameDefinedInRuntime");
var dynamicContext = new MyDbContext(builder.Build(context.Database.Connection).Compile());
For some reason in EF6 it fails on second table request, but mapping inside context looks correct on the moment of execution.
I have a dumb question. It would be great if this could be done, but I am not holding my breath.
I need a single column from a table linked to my JPA entity to be a collection in said JPA entity. Is there any way, that I can just get back that column alone that is related to that entity, instead of having to get back an entire table (which could be very costly?)
Can I perform a query inside that JPA entity that will be performed and loaded eagerly into a collection?
I am trying to avoid having to make several calls to the database by just executing a couple of queries.
What are your thoughts on this?
#ElementCollection(fetch=FetchType.EAGER)
#CollectionTable(name="QUICK_LAUNCH_DISTLIST",joinColumns=#JoinColumn(name="QUICK_LAUNCH_ID"))
#Column(name="LIST_ID")
private List<Long> distListIDs;
The ElementCollection attribute is what I was looking for. It seems to work pretty well in addition to that.
Thanks for the help and inspiration guys.
Suppose a Category has many products:
select product.name from Category c inner join c.products product where ...
If that's not what you want, please show an example in your question.
I've created a function import that returns the results of a stored proceedure as one of my entities. however I can't seem to traverse my through navigation properties to access the data in other entities. I know that you can use include() for objectQueries but can't find anything that will force the EF to load my relations for entity results of function imports.
Any ideas??
Thanks in advance.
This is not possible in EF 1.0
The reason is that EF will consider stored procedure values to be just values and not navigation properites.
For example, Employee entity has multiple Order entities. In Order you have a property called EmployeeID. When the database fills your query using include statements, it creates 1 projection query in SQL to populate all of the Order data that a particular Employee could have.
So if I said
var employee = context.Employees.Include("Orders").Where(e => e.ID == 1).First();
var orders = employee.Orders;
The SQL for the first query will create a projection query which will contain orders where the EmployeeID = 1.
Now when your stored procedure runs, this can do any code behind the scenes (in otherwords it can return any set of data). So when SQL runs the stored procedure, it just runs the code in that stored procedure and does not have any knowledge that EmployeeID on Order is an FK to that property. Additionally, if your stored procedure returns an Employee entity, then you are looking at another scenario where you will not even have an OrderID to pursue.
To work around this though, you can setup your query in EF using Include statements that can mirror any stored procedure. If you use the proper mix of .Select and .Include statements you should be able to do the same thing.