use the predicate in PathElement (#81)

### What

We haven't been using the `predicate` in the
[PathElement](https://hasura.github.io/ndc-spec/reference/types.html#pathelement).
This is no good. We need to use it so we don't produce incorrect results
to users.

### How

We generate a boolean Expression for the predicates using the relevant
tables and we `AND` the resulting Expression with the join predicate in
the `WHERE` clause.

crates/connectors/ndc-citus/tests/query_tests.rs

@@ -232,6 +232,37 @@ mod sorting {
         .await;
         insta::assert_json_snapshot!(result);
     }
+    #[tokio::test]
+    async fn sorting_by_nested_relationship_column_with_predicate() {
+        let result = run_query(
+            create_router().await,
+            "sorting_by_nested_relationship_column_with_predicate",
+        )
+        .await;
+        insta::assert_json_snapshot!(result);
+    }
+
+    // Citus sorts strings differently than PostgreSQL,
+    // so the 5th row might be different.
+    #[tokio::test]
+    async fn sorting_by_nested_relationship_column_with_predicate_exists() {
+        let result = run_query(
+            create_router().await,
+            "sorting_by_nested_relationship_column_with_predicate_exists",
+        )
+        .await;
+        insta::assert_json_snapshot!(result);
+    }
+
+    #[tokio::test]
+    async fn sorting_by_relationship_count_with_predicate() {
+        let result = run_query(
+            create_router().await,
+            "sorting_by_relationship_count_with_predicate",
+        )
+        .await;
+        insta::assert_json_snapshot!(result);
+    }
 }
 
 mod aggregation {

crates/connectors/ndc-citus/tests/snapshots/query_tests__sorting__sorting_by_nested_relationship_column_with_predicate.snap

@@ -0,0 +1,16 @@
+---
+source: crates/connectors/ndc-citus/tests/query_tests.rs
+expression: result
+---
+[
+  {
+    "rows": [
+      {
+        "Name": "Crazy Train"
+      },
+      {
+        "Name": "I Don't Know"
+      }
+    ]
+  }
+]

crates/connectors/ndc-citus/tests/snapshots/query_tests__sorting__sorting_by_nested_relationship_column_with_predicate_exists.snap

@@ -0,0 +1,25 @@
+---
+source: crates/connectors/ndc-citus/tests/query_tests.rs
+expression: result
+---
+[
+  {
+    "rows": [
+      {
+        "Name": "Balls to the Wall"
+      },
+      {
+        "Name": "Fast As a Shark"
+      },
+      {
+        "Name": "Princess of the Dawn"
+      },
+      {
+        "Name": "Restless and Wild"
+      },
+      {
+        "Name": "\"?\""
+      }
+    ]
+  }
+]

crates/connectors/ndc-citus/tests/snapshots/query_tests__sorting__sorting_by_relationship_count_with_predicate.snap

@@ -0,0 +1,25 @@
+---
+source: crates/connectors/ndc-citus/tests/query_tests.rs
+expression: result
+---
+[
+  {
+    "rows": [
+      {
+        "Name": "Iron Maiden"
+      },
+      {
+        "Name": "Metallica"
+      },
+      {
+        "Name": "U2"
+      },
+      {
+        "Name": "Led Zeppelin"
+      },
+      {
+        "Name": "Deep Purple"
+      }
+    ]
+  }
+]

crates/connectors/ndc-cockroach/tests/query_tests.rs

@@ -244,6 +244,22 @@ mod sorting {
         .await;
         insta::assert_json_snapshot!(result);
     }
+
+    // CockroachDB has the opposite default for nulls ordering than PostgreSQL,
+    // making the test I've written return random results
+    // (since most tracks are not by Accept, nulls are returned
+    // first, and we limit the number of results,
+    // we are not going to get the same result here),
+    // so we skip the two other sorting with predicate tests.
+    #[tokio::test]
+    async fn sorting_by_relationship_count_with_predicate() {
+        let result = run_query(
+            create_router().await,
+            "sorting_by_relationship_count_with_predicate",
+        )
+        .await;
+        insta::assert_json_snapshot!(result);
+    }
 }
 
 mod aggregation {

crates/connectors/ndc-cockroach/tests/snapshots/query_tests__sorting__sorting_by_relationship_count_with_predicate.snap

@@ -0,0 +1,25 @@
+---
+source: crates/connectors/ndc-cockroach/tests/query_tests.rs
+expression: result
+---
+[
+  {
+    "rows": [
+      {
+        "Name": "Iron Maiden"
+      },
+      {
+        "Name": "Metallica"
+      },
+      {
+        "Name": "U2"
+      },
+      {
+        "Name": "Led Zeppelin"
+      },
+      {
+        "Name": "Deep Purple"
+      }
+    ]
+  }
+]

crates/connectors/ndc-postgres/tests/query_tests.rs

@@ -247,6 +247,36 @@ mod sorting {
         .await;
         insta::assert_json_snapshot!(result);
     }
+
+    #[tokio::test]
+    async fn sorting_by_nested_relationship_column_with_predicate() {
+        let result = run_query(
+            create_router().await,
+            "sorting_by_nested_relationship_column_with_predicate",
+        )
+        .await;
+        insta::assert_json_snapshot!(result);
+    }
+
+    #[tokio::test]
+    async fn sorting_by_nested_relationship_column_with_predicate_exists() {
+        let result = run_query(
+            create_router().await,
+            "sorting_by_nested_relationship_column_with_predicate_exists",
+        )
+        .await;
+        insta::assert_json_snapshot!(result);
+    }
+
+    #[tokio::test]
+    async fn sorting_by_relationship_count_with_predicate() {
+        let result = run_query(
+            create_router().await,
+            "sorting_by_relationship_count_with_predicate",
+        )
+        .await;
+        insta::assert_json_snapshot!(result);
+    }
 }
 
 #[cfg(test)]

crates/connectors/ndc-postgres/tests/snapshots/query_tests__sorting__sorting_by_nested_relationship_column_with_predicate.snap

@@ -0,0 +1,16 @@
+---
+source: crates/connectors/ndc-postgres/tests/query_tests.rs
+expression: result
+---
+[
+  {
+    "rows": [
+      {
+        "Name": "Crazy Train"
+      },
+      {
+        "Name": "I Don't Know"
+      }
+    ]
+  }
+]

crates/connectors/ndc-postgres/tests/snapshots/query_tests__sorting__sorting_by_nested_relationship_column_with_predicate_exists.snap

@@ -0,0 +1,25 @@
+---
+source: crates/connectors/ndc-postgres/tests/query_tests.rs
+expression: result
+---
+[
+  {
+    "rows": [
+      {
+        "Name": "Balls to the Wall"
+      },
+      {
+        "Name": "Fast As a Shark"
+      },
+      {
+        "Name": "Princess of the Dawn"
+      },
+      {
+        "Name": "Restless and Wild"
+      },
+      {
+        "Name": "\"40\""
+      }
+    ]
+  }
+]

crates/connectors/ndc-postgres/tests/snapshots/query_tests__sorting__sorting_by_relationship_count_with_predicate.snap

@@ -0,0 +1,25 @@
+---
+source: crates/connectors/ndc-postgres/tests/query_tests.rs
+expression: result
+---
+[
+  {
+    "rows": [
+      {
+        "Name": "Iron Maiden"
+      },
+      {
+        "Name": "Metallica"
+      },
+      {
+        "Name": "U2"
+      },
+      {
+        "Name": "Led Zeppelin"
+      },
+      {
+        "Name": "Deep Purple"
+      }
+    ]
+  }
+]