I found that if I use the EntityFunctions.AsNonUnicode function on my partNumber parameter it works.
I never had this issue with ADO.NET database queries.
Do I need to call this function on all my parameters, or is there some other course of action to take within the entity framework or database configuration?
There was an ODP.NET 11.2 issue resolved by using EntityFunctions.AsNonUnicode, which was fixed in ODAC 12c. Though, this particular issue was more performance related. What version are you currently using? If it's an 11g version, you may want to try upgrading to see if it resolves this issue.
I am using 22.214.171.124.20 with Entity Framework 5 on an 11g Database.
ODP.NET 126.96.36.199.20 does not have the AsNonUnicode bug fix. Try using ODAC 12c.