diff --git a/api/src/db/models/foreign/attachment.py b/api/src/db/models/foreign/attachment.py
index f7cd98a4b..ced7b1e1d 100644
--- a/api/src/db/models/foreign/attachment.py
+++ b/api/src/db/models/foreign/attachment.py
@@ -5,10 +5,21 @@
 # match by oracle_fdw, but we are matching them for maintainability.
 #
 
+from sqlalchemy.orm import Mapped, foreign, relationship
+
 from src.db.models.legacy_mixin import synopsis_mixin
 
 from . import foreignbase
+from .opportunity import Topportunity
 
 
-class tsynopsisattachment(foreignbase.ForeignBase, synopsis_mixin.TsynopsisAttachmentMixin):
+class TsynopsisAttachment(foreignbase.ForeignBase, synopsis_mixin.TsynopsisAttachmentMixin):
     __tablename__ = "tsynopsisattachment"
+
+    opportunity: Mapped[Topportunity | None] = relationship(
+        Topportunity,
+        primaryjoin=lambda: TsynopsisAttachment.opportunity_id
+        == foreign(Topportunity.opportunity_id),
+        uselist=False,
+        overlaps="opportunity",
+    )
diff --git a/api/src/db/models/staging/attachment.py b/api/src/db/models/staging/attachment.py
index 12e4512a5..f6349cdb3 100644
--- a/api/src/db/models/staging/attachment.py
+++ b/api/src/db/models/staging/attachment.py
@@ -1,6 +1,18 @@
+from sqlalchemy.orm import Mapped, foreign, relationship
+
 from src.db.models.legacy_mixin import synopsis_mixin
 from src.db.models.staging.staging_base import StagingBase, StagingParamMixin
 
+from .opportunity import Topportunity
+
 
 class TsynopsisAttachment(StagingBase, synopsis_mixin.TsynopsisAttachmentMixin, StagingParamMixin):
     __tablename__ = "tsynopsisattachment"
+
+    opportunity: Mapped[Topportunity | None] = relationship(
+        Topportunity,
+        primaryjoin=lambda: TsynopsisAttachment.opportunity_id
+        == foreign(Topportunity.opportunity_id),
+        uselist=False,
+        overlaps="opportunity",
+    )
diff --git a/api/tests/src/data_migration/transformation/subtask/test_transform_opportunity_attachment.py b/api/tests/src/data_migration/transformation/subtask/test_transform_opportunity_attachment.py
new file mode 100644
index 000000000..0c9895e89
--- /dev/null
+++ b/api/tests/src/data_migration/transformation/subtask/test_transform_opportunity_attachment.py
@@ -0,0 +1,41 @@
+from src.db.models.foreign.attachment import TsynopsisAttachment as TsynopsisAttachmentF
+from src.db.models.staging.attachment import TsynopsisAttachment as TsynopsisAttachmentS
+from tests.src.db.models.factories import (
+    ForeignTsynopsisAttachmentFactory,
+    StagingTsynopsisAttachmentFactory,
+)
+
+
+def test_uploading_attachment_staging(db_session, enable_factory_create, tmp_path):
+    att = StagingTsynopsisAttachmentFactory.create(file_lob=b"Testing attachment")
+    db_session.commit()
+    db_session.expire_all()
+
+    db_att = (
+        db_session.query(TsynopsisAttachmentS)
+        .filter(TsynopsisAttachmentS.opportunity_id == att.opportunity_id)
+        .one_or_none()
+    )
+    temp_file = tmp_path / "out_file.txt"
+    temp_file.write_bytes(db_att.file_lob)
+    file_content = temp_file.read_bytes()
+
+    assert file_content == db_att.file_lob
+
+
+def test_uploading_attachment_foreign(db_session, enable_factory_create, tmp_path):
+    att = ForeignTsynopsisAttachmentFactory.create(file_lob=b"Testing attachment")
+    db_session.commit()
+    db_session.expire_all()
+
+    db_att = (
+        db_session.query(TsynopsisAttachmentF)
+        .filter(TsynopsisAttachmentF.opportunity_id == att.opportunity_id)
+        .one_or_none()
+    )
+
+    temp_file = tmp_path / "out_file.txt"
+    temp_file.write_bytes(db_att.file_lob)
+    file_content = temp_file.read_bytes()
+
+    assert file_content == db_att.file_lob
diff --git a/api/tests/src/db/models/factories.py b/api/tests/src/db/models/factories.py
index 677f32911..09218fc6c 100644
--- a/api/tests/src/db/models/factories.py
+++ b/api/tests/src/db/models/factories.py
@@ -997,6 +997,32 @@ class Meta:
     publisher_profile_id = sometimes_none(factory.Faker("random_int", min=1, max=99_999))
 
 
+class TsynopsisAttachmentFactory(BaseFactory):
+    class Meta:
+        abstract = True
+
+    syn_att_id: factory.Sequence(lambda n: n)
+    opportunity_id: factory.Sequence(lambda n: n)
+    att_revision_number = factory.Faker("random_int", min=1000, max=10000000)
+    att_type: factory.Faker("att_type")
+    mime_type = factory.Faker("mime_type")
+    link_url = factory.Faker("relevant_url")
+    file_name = factory.Faker("file_name")
+    file_desc = factory.Faker("sentence")
+    file_lob = b"Test attachment"
+    file_lob_size = factory.LazyAttribute(lambda x: len(x.file_lob))
+    create_date = factory.Faker("date_time_between", start_date="-1y", end_date="now")
+    created_date = factory.LazyAttribute(
+        lambda o: fake.date_time_between(start_date=o.create_date, end_date="now")
+    )
+    last_upd_date = factory.LazyAttribute(
+        lambda o: fake.date_time_between(start_date=o.created_date, end_date="now")
+    )
+    creator_id = factory.Faker("first_name")
+    last_upd_id = factory.Faker("first_name")
+    syn_att_folder_id = factory.Faker("random_int", min=1000, max=10000000)
+
+
 class TforecastFactory(BaseFactory):
     class Meta:
         abstract = True
@@ -1363,6 +1389,14 @@ class Meta:
     creator_id = factory.Faker("first_name")
 
 
+class StagingTsynopsisAttachmentFactory(TsynopsisAttachmentFactory, AbstractStagingFactory):
+    class Meta:
+        model = staging.attachment.TsynopsisAttachment
+
+    opportunity = factory.SubFactory(StagingTopportunityFactory)
+    opportunity_id = factory.LazyAttribute(lambda o: o.opportunity.opportunity_id)
+
+
 ####################################
 # Transfer Table Factories
 ####################################
@@ -1593,6 +1627,14 @@ class Meta:
     revision_number = factory.LazyAttribute(lambda s: s.synopsis.revision_number)
 
 
+class ForeignTsynopsisAttachmentFactory(TsynopsisAttachmentFactory):
+    class Meta:
+        model = foreign.attachment.TsynopsisAttachment
+
+    opportunity = factory.SubFactory(ForeignTopportunityFactory)
+    opportunity_id = factory.LazyAttribute(lambda o: o.opportunity.opportunity_id)
+
+
 ##
 # Pseudo-factories
 ##
diff --git a/documentation/api/database/erds/staging-schema.png b/documentation/api/database/erds/staging-schema.png
index 1bfae06eb..f4771f887 100644
Binary files a/documentation/api/database/erds/staging-schema.png and b/documentation/api/database/erds/staging-schema.png differ