.prepare vs. .select - swift

Question

I have a working connection to a database in an iOS10 app, using SQLite.swift.
I want to select details for a specific university where I have an IHE_ID passed in from another view controller.
I would like to just select the row for that specific university, but I can't get a query to work. I can however loop through all the data with a prepare and then choose the one I need from that, which of course is more resource intensive than I need since I already have the specific IHE_ID passed in as anIHE Int from the sending view controller.
connection is working so omitting that code...
do {
let db = try Connection(destinationDBPath, readonly: true)
let IHEs = Table("IHE")
let IHE_ID = Expression<Int>("IHE_ID")
let IHE_Name = Expression<String>("IHE_Name")
let IHE_COE_Url = Expression<String>("IHE_COE_URL")
let IHE_Sector = Expression<Int>("IHE_Sector")
let IHE_COE_Name = Expression<String>("IHE_COE_Name")
for ihe in try db.prepare(IHEs){
if (ihe[IHE_ID] == anIHE){
// build this string, otherwise ignore rest of dataset (doing this because query isn't working)
buildIHE = "Name: \(ihe[IHE_Name])\n"
buildIHE.append("URL: \(ihe[IHE_COE_Url])\n")
// buildIHE.append("Sector: \(ihe[IHE_Sector])\n")
if (ihe[IHE_Sector] == 0) {
buildIHE.append("Sector: Public\n")
} else {
buildIHE.append("Sector: Private\n")
}
buildIHE.append("College of Education Name: \(ihe[IHE_COE_Name])\n")
}
}
print ("Got through building IHE portion of view")
What I'd like to do is use this instead of the for loop.
if let query = IHEs.select(IHE_ID,IHE_Name,IHE_COE_Url,IHE_Sector,IHE_COE_Name).filter(IHE_ID == anIHE){
print("Query successful for \(anIHE) with name \(query[IHE_Name])")
// more actions to build the string I need would then occur
} else {
print("Query has failed or returned nil")
}
Finally, I'll use the selected elements if I can get the query to work.
I think I probably just have something wrong with my syntax on the query, but any help is appreciated.
The line with the "if let query" has this error in Xcode:
Initializer for conditional binding must have Optional type, not 'Table'.
This leads me to think it's something with my use of the .select statement and just new to using SQLite.swift and swift in general.
Last thing is that anIHE comes into this function as an Int, and IHE_ID is Expression as shown in this code. I'm thinking this may be part of the problem.

Answer 1

The Initializer for conditional binding must have Optional type error means that the expression on the right of the if let v = expr statement is not an Optional: there is no point using if let, and the Swift compiler says that you should just write let v = expr.
And indeed, IHEs.select(...).filter(...) returns a non-optional value of type Table.
It is not the database row you expect, because the query has been defined, but not executed yet. After all, you weren't using db: where would the rows be loaded from?
The solution is to bring back the database connection, and load a single row. This is done with the pluck method.
if let ihe = try db.pluck(IHEs.select(...).filter(...)) {
print("Name \(ihe[IHE_Name])")
}