Optimize database queries and file handling in content serializers

[noissue]

pulp_deb/app/serializers/content_serializers.py

@@ -488,13 +488,10 @@ def to822(self, component=""):
             artifact = RemoteArtifact.objects.filter(sha256=self.instance.sha256).first()
 
         if artifact:
-            if artifact.md5:
-                ret["MD5sum"] = artifact.md5
-            if artifact.sha1:
-                ret["SHA1"] = artifact.sha1
+            ret["MD5sum"] = artifact.md5 if artifact.md5 else None
+            ret["SHA1"] = artifact.sha1 if artifact.sha1 else None
             ret["SHA256"] = artifact.sha256
             ret["Size"] = str(artifact.size)
-
         ret["Filename"] = self.instance.filename(component)
 
         return ret
@@ -600,24 +597,21 @@ def deferred_validate(self, data):
         data = super().deferred_validate(data)
 
         try:
-            package_paragraph = debfile.DebFile(fileobj=data["artifact"].file).debcontrol()
+            with debfile.DebFile(fileobj=data["artifact"].file) as deb_file:
+                package_paragraph = deb_file.debcontrol()
         except debfile.DebError as e:
-            if "[Errno 2] No such file or directory: 'unzstd'" in "{}".format(e):
-                message = (
-                    "The package file provided uses zstd compression, but the unzstd binary is not "
-                    "available! Make sure the zstd package (depending on your package manager) is "
-                    "installed."
-                )
-            else:
-                message = (
-                    "python-debian was unable to read the provided package file! The error is '{}'."
+            error_message = str(e)
+            if "unzstd" in error_message:
+                raise ValidationError(
+                    _("The package file used zstd compression, but 'unzstd' is not available!")
                 )
-            raise ValidationError(_(message).format(e))
+            raise ValidationError(_("Failed to read the package file: {}").format(error_message))
 
         from822_serializer = self.Meta.from822_serializer.from822(data=package_paragraph)
         from822_serializer.is_valid(raise_exception=True)
         package_data = from822_serializer.validated_data
         data.update(package_data)
+
         data["sha256"] = data["artifact"].sha256
 
         if "relative_path" not in data:
@@ -633,9 +627,9 @@ def deferred_validate(self, data):
     def retrieve(self, validated_data):
         content = self.Meta.model.objects.filter(
             sha256=validated_data["sha256"], relative_path=validated_data["relative_path"]
-        )
+        ).first()
 
-        return content.first()
+        return content
 
     class Meta:
         fields = (
@@ -1218,16 +1212,16 @@ def deferred_validate(self, data):
 
         artifacts = {data["relative_path"]: data["artifact"]}
         for source in data["checksums_sha256"]:
-            content = Artifact.objects.filter(sha256=source["sha256"], size=source["size"])
-            if not content.exists():
+            content = Artifact.objects.get(sha256=source["sha256"], size=source["size"])
+            if not content:
                 raise ValidationError(
                     _(
                         "A source file is listed in the DSC file but is not yet available '{name}'"
                         " and sha256 '{sha256}'."
                     ).format(name=source["name"], sha256=source["sha256"])
                 )
             artifacts[os.path.join(os.path.dirname(data["relative_path"]), source["name"])] = (
-                content.first()
+                content
             )
 
         data["artifacts"] = artifacts
@@ -1237,7 +1231,11 @@ def retrieve(self, data):
         """
         If the Source Package already exists, retrieve it
         """
-        return SourcePackage.objects.filter(source=data["source"], version=data["version"]).first()
+        return (
+            SourcePackage.objects.only("source", "version")
+            .filter(source=data["source"], version=data["version"])
+            .first()
+        )
 
     class Meta:
         fields = MultipleArtifactContentSerializer.Meta.fields + (