add env var for forcing relation strategy

query-engine/core/src/query_graph_builder/read/utils.rs

@@ -1,5 +1,6 @@
 use super::*;
 use crate::{ArgumentListLookup, FieldPair, ParsedField, ReadQuery};
+use once_cell::sync::Lazy;
 use psl::datamodel_connector::{ConnectorCapability, JoinStrategySupport};
 use query_structure::{native_distinct_compatible_with_order_by, prelude::*, RelationLoadStrategy};
 use schema::{
@@ -259,6 +260,13 @@ pub(crate) fn get_relation_load_strategy(
     nested_queries: &[ReadQuery],
     query_schema: &QuerySchema,
 ) -> QueryGraphBuilderResult<RelationLoadStrategy> {
+    static RELATION_LOAD_STRATEGY: Lazy<Result<RelationLoadStrategy, DomainError>> =
+        Lazy::new(|| std::env::var("RELATION_LOAD_STRATEGY").unwrap().as_str().try_into());
+
+    if RELATION_LOAD_STRATEGY.is_ok() {
+        return Ok(*RELATION_LOAD_STRATEGY.as_ref().unwrap());
+    }
+
     match query_schema.join_strategy_support() {
         // Connector and database version supports the `Join` strategy...
         JoinStrategySupport::Yes => match requested_strategy {

query-engine/query-structure/src/query_arguments.rs

@@ -40,6 +40,21 @@ impl RelationLoadStrategy {
     }
 }
 
+impl TryFrom<&str> for RelationLoadStrategy {
+    type Error = crate::error::DomainError;
+
+    fn try_from(value: &str) -> crate::Result<Self> {
+        match value {
+            "join" => Ok(RelationLoadStrategy::Join),
+            "query" => Ok(RelationLoadStrategy::Query),
+            _ => Err(DomainError::ConversionFailure(
+                value.to_owned(),
+                "RelationLoadStrategy".to_owned(),
+            )),
+        }
+    }
+}
+
 impl std::fmt::Debug for QueryArguments {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         f.debug_struct("QueryArguments")