How to search Oracle table with a string key using Entity Framework 5 and the ODP.NET Managed Provider - oracle

Question

My table is like this (pseudo code):
CREATE TABLE DOCUMENT_LOCATOR (DOCUMENT_ID VARCHAR2(6) PRIMARY KEY)
When using the latest ODP.NET Managed Driver v121.1.2 downloaded via NuGet, the following Entity Framework commands do NOT use the index:
context.DOCUMENT_LOCATOR.Find("ABC123");
context.DOCUMENT_LOCATOR.Find(EntityFunctions.AsNonUnicode("ABC123"));
context.DOCUMENT_LOCATOR.FirstOrDefault(i => i.DOCUMENT_ID == "ABC123");
The following command does use the index:
context.DOCUMENT_LOCATOR.FirstOrDefault(i => i.DOCUMENT_ID == EntityFunctions.AsNonUnicode("ABC123"));
Unfortunately, UPDATEs and DELETEs do not use the index, so they basically render EF/Oracle useless for large tables. Has anyone figured out how to work around this?

Answer 1

After a fair amount of searching, I found a very nice solution. It sets all the string properties of all the entities to IsUnicode(false). To use it, you simply add one line to the OnModelCreating method of your DbContext class:
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Configurations.Add(new ASSUMED_NAME_FILESMap());
modelBuilder.Configurations.Add(new ASSUMED_NAME_FILENAME_ONLYMap());
modelBuilder.Configurations.Add(new DOCUMENT_LOCATORMap());
modelBuilder.Configurations.Add(new IMS_IMAGE_TABLEMap());
modelBuilder.DisableUnicodeForAllEntityStrings(this);
}
As you can see, I changed the code to be an extension. Here's my adapted code:
public static class DbModelBuilderExtensions
{
/// <summary>
/// Disables unicode for all string properties on entities in the given context.
/// MUST BE CALLED AFTER modelBuilder.Configurations.Add(map) CALLS.
/// </summary>
/// <remarks>
/// Adapted from http://www.johncoder.com/Post/EFCodeFirstDisableUnicodeforallStringProperties
/// </remarks>
public static void DisableUnicodeForAllEntityStrings(this DbModelBuilder builder, DbContext context)
{
// Get all IDbSet<> properties from the context
var entityTypes = from property in context.GetType().GetProperties()
where property.PropertyType.ImplementsInterface(typeof(IDbSet<>))
let entityType = property.PropertyType.GetGenericArguments()[0]
select entityType;
// Disable Unicode support for each table
foreach (var entityType in entityTypes)
DisableUnicodeForEntityStrings(builder, entityType);
}
private static void DisableUnicodeForEntityStrings(DbModelBuilder modelBuilder, Type entityType)
{
// Get all string properties with setters
var stringProperties = from property in entityType.GetProperties()
where property.PropertyType == typeof(string)
&& property.CanWrite
select property;
// Each table field must be varchar for now,
// so take the string property & call IsUnicode(false).
foreach (var property in stringProperties)
{
// Don't remove this line.
// Lambda might not work without it.
PropertyInfo prop = property;
// Create the correct expression type,
// should be Expression<Func<TModel, string>>
var exprType = typeof(Expression<>)
.MakeGenericType(typeof(Func<,>)
.MakeGenericType(prop.ReflectedType, typeof(string)));
// Find and execute the Entity() method,
// using TModel generic parameter
var obj = modelBuilder.GetType()
.GetMethod("Entity")
.MakeGenericMethod(prop.ReflectedType)
.Invoke(modelBuilder, null);
// Runtime Lambda expression to represent
// something like Property(p => p.Suffix)
ParameterExpression pe = Expression.Parameter(prop.ReflectedType, "p");
var expression = Expression.Lambda(Expression.Property(pe, prop.Name), pe);
// Find the Property method that takes an expression as a parameter
// and then invoke it using the expression that was just built
var p = obj.GetType()
.GetMethod("Property", new[] { exprType })
.Invoke(obj, new[] { expression });
// If all goes well, we'll have a StringPropertyConfiguration.
var propertyConfig = p as StringPropertyConfiguration;
if (propertyConfig != null)
propertyConfig.IsUnicode(false);
}
}
public static bool ImplementsInterface(this Type value, Type interfaceType)
{
return value.GetInterface(interfaceType.FullName) != null;
}
}