add better implementation for checking if collections are empty in ti…

…me controller

Project.toml

@@ -1,6 +1,6 @@
 name = "PSRClassesInterface"
 uuid = "1eab49e5-27d8-4905-b9f6-327b6ea666c4"
-version = "0.17.1"
+version = "0.17.2"
 
 [deps]
 DBInterface = "a10d1c49-ce27-4219-8d33-6db1a4562965"

src/PSRDatabaseSQLite/read.jl

@@ -15,10 +15,6 @@ function number_of_elements(db::DatabaseSQLite, collection_id::String)::Int
     end
 end
 
-function _collection_has_any_data(db::DatabaseSQLite, collection_id::String)::Bool
-    return number_of_elements(db, collection_id) > 0
-end
-
 function _get_id(
     db::DatabaseSQLite,
     collection_id::String,
@@ -391,7 +387,7 @@ function read_time_series_row(
 
     T = attribute.type
 
-    if !(_collection_has_any_data(db, collection_id))
+    if !(_time_controller_collection_has_any_data(db, collection_id))
         return Vector{T}(undef, 0)
     end
     if !haskey(db._time_controller.cache, collection_attribute)

src/PSRDatabaseSQLite/time_controller.jl

@@ -20,18 +20,35 @@ mutable struct TimeControllerCache{T}
     _closest_global_previous_date_with_data::DateTime
     _closest_global_next_date_with_data::DateTime
 
-    # Cache of collection_ids
+    # Cache of collection_ids, these are the ids of elements in a specific collection
     _collection_ids::Vector{Int}
 end
 
 Base.@kwdef mutable struct TimeController
     cache::Dict{CollectionAttribute, TimeControllerCache} = Dict{CollectionAttribute, TimeControllerCache}()
+
+    # Upon initialization the time controller will ask if a certain 
+    # collection has any elements, if the collection has any elements it 
+    # will be added to this cache. This cache will be used to avoid querying
+    # multiple times if a certain collection has any elements.
+    # This relies on the fact that the Time Controller only works in 
+    # read only databases.
+    collection_has_any_data::Dict{String, Bool} = Dict{String, Bool}()
 end
 
 function _collection_attribute(collection_id::String, attribute_id::String)::CollectionAttribute
     return (collection_id, attribute_id)
 end
 
+function _time_controller_collection_has_any_data(db, collection_id::String)::Bool
+    if haskey(db._time_controller.collection_has_any_data, collection_id)
+        return db._time_controller.collection_has_any_data[collection_id]
+    else
+        db._time_controller.collection_has_any_data[collection_id] = number_of_elements(db, collection_id) > 0
+        return db._time_controller.collection_has_any_data[collection_id]
+    end
+end
+
 function _update_time_controller_cache!(
     cache::TimeControllerCache,
     db,