Swift concatenate string based on different values - ios

Question

I need to concatenate a string based on some logic but I cant figure out how to do it.
Example:
var filterString: String = ""
var hasFilter: Bool = false
if let catId = param["catid"] {
filterString += "cat_id=\(catId)"
hasFilter = true
}
if let subCatId = param["subcatid"] {
filterString += "sub_cat_id=\(subCatId)"
hasFilter = true
}
if let locationId = param["stateid"] {
filterString += "location_id=\(locationId)"
hasFilter = true
}
if hasFilter == true {
query.filters = filterString
}
This will only work if I have ONE filter in my query
Eg: query.filters = "location_id=4"
But if I happend to have two or more filters my query will break eg:
query.filters = "location_id=4cat_id=3"
If I have more then one filter I need to seperate it with a AND statement like this:
query.filters = "location_id=4 AND cat_id=3"
But I cant figure out how to do it since I never know what order the filter will come in or if there even will be one or more filters to begin with
Edit
I seem to get it working by:
var filterString: String = ""
var hasFilter: Bool = false
if let catId = param["catid"] {
filterString += "cat_id=\(catId)"
hasFilter = true
}
if let subCatId = param["subcatid"] {
if hasFilter == true {
filterString += " AND sub_cat_id=\(subCatId)"
} else {
filterString += "sub_cat_id=\(subCatId)"
}
hasFilter = true
}
if let locationId = param["stateid"] {
if hasFilter == true {
filterString += " AND location_id=\(locationId)"
} else {
filterString += "location_id=\(locationId)"
}
hasFilter = true
}
if hasFilter == true {
query.filters = filterString
}

Answer 1

One solution would be to put the filters into an array and then if the array isn't empty, combine the array values with an " AND " separator.
var filters : [String] = []
if let catId = param["catid"] {
filters.append("cat_id=\(catId)")
}
if let subCatId = param["subcatid"] {
filters.append("sub_cat_id=\(subCatId)")
}
if let locationId = param["stateid"] {
filters.append("location_id=\(locationId)")
}
if filters.count > 0 {
query.filters = filters.joined(separator: " AND ")
}

Answer 2

Maybe you can first create an array and append all the filters.
After that create another variable to append all the values in the array.

Answer 3

Another option using inline if statements:
var param = ["catid" : "111", "subcatid" : "222", "stateid" : "333"]
var filterString = ""
if let catId = param["catid"] {
filterString = "cat_id=\(catId)"
}
if let subCatId = param["subcatid"] {
filterString.appendContentsOf(filterString.characters.count > 0 ? " AND sub_cat_id=\(subCatId)" : "sub_cat_id=\(subCatId)")
}
if let locationId = param["stateid"] {
filterString.appendContentsOf(filterString.characters.count > 0 ? " AND location_id=\(locationId)" : "location_id=\(locationId)")
}
print(filterString)
if (filterString.characters.count > 0) {
query.filters = filterString
}