fix pkey name overflow in _drop_primary_key

timescale/db/backends/postgis/schema.py

@@ -77,7 +77,8 @@ def _drop_primary_key(self, model):
         """
         db_table = model._meta.db_table
         table = self.quote_name(db_table)
-        pkey = self.quote_name(f'{db_table}_pkey')
+        pkey_length = self.connection.ops.max_name_length()
+        pkey = self.quote_name(f'{db_table[:pkey_length - 5]}_pkey')
 
         sql = self.sql_drop_primary_key.format(table=table, pkey=pkey)
 

timescale/db/backends/postgresql/schema.py

@@ -78,7 +78,8 @@ def _drop_primary_key(self, model):
         """
         db_table = model._meta.db_table
         table = self.quote_name(db_table)
-        pkey = self.quote_name(f'{db_table}_pkey')
+        pkey_length = self.connection.ops.max_name_length()
+        pkey = self.quote_name(f'{db_table[:pkey_length - 5]}_pkey')
 
         sql = self.sql_drop_primary_key.format(table=table, pkey=pkey)
 

timescale/db/models/aggregates.py

@@ -22,6 +22,20 @@ def __init__(self, expression, min_value, max_value, bucket):
         super().__init__(expression, min_value, max_value, bucket)
 
 
+class LTTB(models.Func):
+    function = 'lttb'
+    name = 'lttb'
+    output_field = models.DateTimeField()
+
+    def __init__(self, time, value, count, field):
+        self.fieldname = field
+        super().__init__(time, value, count)
+
+    def as_sql(self, compiler, connection, **extra_context):
+        sql, params = super().as_sql(compiler, connection, **extra_context)
+        return f'(unnest({sql})).{self.fieldname}', params
+
+
 class Last(models.Aggregate):
     function = 'last'
     name = 'last'

timescale/db/models/managers.py

@@ -23,3 +23,6 @@ def time_bucket_gapfill(self, field: str, interval: str, start: datetime, end: d
 
     def histogram(self, field: str, min_value: float, max_value: float, num_of_buckets: int = 5):
         return self.get_queryset().histogram(field, min_value, max_value, num_of_buckets)
+
+    def lttb(self, time: str, value: str, num_of_counts: int = 20):
+        return self.get_queryset().lttb(time, value, num_of_counts)

timescale/db/models/querysets.py

@@ -1,6 +1,6 @@
 from django.db import models
 from timescale.db.models.expressions import TimeBucket, TimeBucketGapFill, TimeBucketNG
-from timescale.db.models.aggregates import Histogram
+from timescale.db.models.aggregates import Histogram, LTTB
 from typing import Dict, Optional
 from datetime import datetime
 
@@ -35,6 +35,15 @@ def histogram(self, field: str, min_value: float, max_value: float, num_of_bucke
         """
         return self.values(histogram=Histogram(field, min_value, max_value, num_of_buckets))
 
+    def lttb(self, time: str, value: str, num_of_counts: int = 20):
+        """
+        Wraps the TimescaleDB toolkit lttb function into a queryset method.
+        """
+        return self.values(
+            lttb_t=LTTB(time, value, num_of_counts, time),
+            lttb_v=LTTB(time, value, num_of_counts, value)
+        )
+
     def to_list(self, normalise_datetimes: bool = False):
         if normalise_datetimes:
             normalised = []