Making a query and adding the result to a struct with Swift

Question

Based on SQLite tutorial for Swift (Link), I am able to perform a query successfully as follows (with a raw query):

struct myStruct {
   var value1 = String()
   var value2 = String()
   var value3 = String()
   var value4 = String()
}

do {
   guard let queryResults = try? db.prepare("SELECT value1, value2, value3, value4 FROM table WHERE identifier = 0")
   else {
      print("ERROR")
      return
   }
   //first way to get data (works)
   for row in queryResults {
      let data = myStruct(value1: row[0] as! String, value2: row[1] as! String, value3: "", eventDate: row[2] as! String, value4: row[3] as! String)
      tableViewData.append(data)
   }
   //second way to get data into struct     
   _ = queryResults.map { row in
       let data = myStruct(value1: row[0]! as! String, value2: row[1] as! String, value3: "", eventDate: row[2] as! String, value4: row[3] as! String)
       tableViewData.append(data)
   }
}
catch let ex {
   print("ReadDB error: \(ex)")
}

But, if I change the style of the query as follows:

do {
   let query = myTable.select(value1, value2, value3, value4).where(identifier == 0)
   guard let queryResults = try? db.prepare(query)
   else {
      print("ERROR")
      return
   }
   //does not work
   for row in queryResults {
      let data = myStruct(value1: row[0] as! String, value2: row[1] as! String, value3: "", eventDate: row[2] as! String, value4: row[3] as! String)
      tableViewData.append(data)
   }
   //neither working   
   _ = queryResults.map { row in
       let data = myStruct(value1: row[0]! as! String, value2: row[1] as! String, value3: "", eventDate: row[2] as! String, value4: row[3] as! String)
       tableViewData.append(data)
   }
}
catch let ex {
   print("ReadDB error: \(ex)")
}

I get this error:

Cannot subscript a value of type 'Row' with an index of type 'Int'

Can anyone help me with this?

Sure... github.com/stephencelis/SQLite.swift/blob/master/Documentation/… — Ricardo Isidro
– Ricardo Isidro, Commented Nov 29, 2018 at 19:03

Ricardo Isidro · Accepted Answer · 2018-11-29 20:05:27Z

2

This is the right way

do {
   let query = myTable.select(value1, value2, value3, value4).where(identifier == 0)
   guard let queryResults = try? db.prepare(query)
   else {
      print("ERROR")
      return
   }
   //option 1
   for row in queryResults {
      let data = myStruct(value1: try row.get(value1), value2: try row.get(value2), value3: try row.get(value3), value4: try row.get(value4))
      tableViewData.append(data)
   }
   //option 2  
   _ = queryResults.map { row in
       let data = myStruct(value1: try row.get(value1), value2: try row.get(value2), value3: try row.get(value3), value4: try row.get(value4))
       tableViewData.append(data)
   }
}
catch let ex {
   print("ReadDB error: \(ex)")
}

answered Nov 29, 2018 at 20:05

Ricardo Isidro

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Comments

impression7vx · Accepted Answer · 2018-11-29 19:11:16Z

From the tutorial, it seems that something like

//This is from tutorial

let query = users.select(email)           // SELECT "email" FROM "users"
             .filter(name != nil)     // WHERE "name" IS NOT NULL
             .order(email.desc, name) // ORDER BY "email" DESC, "name"
             .limit(5, offset: 1)     // LIMIT 5 OFFSET 1

That .select(item) actually IS the query itself. So, whenever you do

let query = myTable.select(value1, value2, value3, value4).where(identifier == 0) then THIS is the query; you don't need to prepare anything for the db. The person(s) who created this library has tried to make it easier whereas you can just do .select(item) instead of creating a statement and sending it to a db.

Using the example above, you can see that the query selects email, where it is filtered, ordered, and limited. Therefore, for you, query is what you want as queryResult -- I am not sure what that would return... You would be running the result of query on db.prepare(query)...hrm? :P

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