Add 'has subtasks' filter

app/src/main/java/com/todoroo/andlib/sql/Operator.kt

@@ -6,6 +6,7 @@ class Operator private constructor(private val operator: String) {
     companion object {
         val eq = Operator("=")
         val isNull = Operator("IS NULL")
+        val isNotNull = Operator("IS NOT NULL")
         val and = Operator("AND")
         val or = Operator("OR")
         val not = Operator("NOT")

app/src/main/java/com/todoroo/andlib/sql/UnaryCriterion.kt

@@ -25,6 +25,12 @@ open class UnaryCriterion private constructor(private val expression: Field, ope
 
         fun lte(field: Field, value: Any?): Criterion = UnaryCriterion(field, Operator.lte, value)
 
+        fun isNotNull(field: Field): Criterion {
+            return object : UnaryCriterion(field, Operator.isNotNull, null) {
+                override fun populateOperator() = " $operator"
+            }
+        }
+
         fun isNull(field: Field): Criterion {
             return object : UnaryCriterion(field, Operator.isNull, null) {
                 override fun populateOperator() = " $operator"

app/src/main/java/org/tasks/filters/FilterCriteriaProvider.kt

@@ -7,6 +7,7 @@ import com.todoroo.andlib.sql.Field.Companion.field
 import com.todoroo.andlib.sql.Join.Companion.inner
 import com.todoroo.andlib.sql.Join.Companion.left
 import com.todoroo.andlib.sql.Query.Companion.select
+import com.todoroo.andlib.sql.UnaryCriterion.Companion.isNotNull
 import com.todoroo.astrid.api.*
 import com.todoroo.astrid.data.Task
 import dagger.hilt.android.qualifiers.ApplicationContext
@@ -36,6 +37,7 @@ class FilterCriteriaProvider @Inject constructor(
             IDENTIFIER_RECUR -> recurringFilter
             IDENTIFIER_COMPLETED -> completedFilter
             IDENTIFIER_HIDDEN -> hiddenFilter
+            IDENTIFIER_PARENT -> parentFilter
             IDENTIFIER_SUBTASK -> subtaskFilter
             else -> throw RuntimeException("Unknown identifier: $identifier")
         }
@@ -65,6 +67,7 @@ class FilterCriteriaProvider @Inject constructor(
         result.add(recurringFilter)
         result.add(completedFilter)
         result.add(hiddenFilter)
+        result.add(parentFilter)
         result.add(subtaskFilter)
         return result
     }
@@ -123,6 +126,21 @@ class FilterCriteriaProvider @Inject constructor(
                         .toString()
         )
 
+    private val parentFilter: CustomFilterCriterion
+    get() = BooleanCriterion(
+            IDENTIFIER_PARENT,
+            context.getString(R.string.custom_filter_has_subtask),
+            select(Task.ID)
+                    .from(Task.TABLE)
+                    .join(left(Task.TABLE.`as`("children"), Task.ID.eq(field("children.parent"))))
+                    .join(left(GoogleTask.TABLE, GoogleTask.PARENT.eq(Task.ID)))
+                    .where(or(
+                            isNotNull(field("children._id")),
+                            isNotNull(GoogleTask.ID)
+                    ))
+                    .toString()
+    )
+
     private val subtaskFilter: CustomFilterCriterion
         get() = BooleanCriterion(
                 IDENTIFIER_SUBTASK,
@@ -282,6 +300,7 @@ class FilterCriteriaProvider @Inject constructor(
         private const val IDENTIFIER_RECUR = "recur"
         private const val IDENTIFIER_COMPLETED = "completed"
         private const val IDENTIFIER_HIDDEN = "hidden"
+        private const val IDENTIFIER_PARENT = "parent"
         private const val IDENTIFIER_SUBTASK = "subtask"
     }
 }

app/src/main/res/values/strings.xml

@@ -656,5 +656,6 @@ File %1$s contained %2$s.\n\n
   <string name="multi_select_reschedule">Reschedule</string>
   <string name="date_picker_multiple">Multiple</string>
   <string name="delete_comment">Delete this comment?</string>
+  <string name="custom_filter_has_subtask">Has subtasks</string>
   <string name="custom_filter_is_subtask">Is subtask</string>
 </resources>