Index: django/db/models/query.py
===================================================================
--- django/db/models/query.py	(revision 5800)
+++ django/db/models/query.py	(working copy)
@@ -777,7 +777,7 @@
             return SortedDict(), [], []
         return joins, where2, params
 
-def get_where_clause(lookup_type, table_prefix, field_name, value):
+def get_where_clause(lookup_type, table_prefix, field_name, value, db_type):
     if table_prefix.endswith('.'):
         table_prefix = backend.quote_name(table_prefix[:-1])+'.'
     field_name = backend.quote_name(field_name)
@@ -785,36 +785,41 @@
         cast_sql = backend.get_datetime_cast_sql()
     else:
         cast_sql = '%s'
+    if hasattr(backend, 'get_field_cast_sql'):
+        field_cast_sql = backend.get_field_cast_sql(db_type)
+    else:
+        field_cast_sql = '%s%s'
+    field_sql = field_cast_sql % (table_prefix, field_name)
     if lookup_type in ('iexact', 'icontains', 'istartswith', 'iendswith') and backend.needs_upper_for_iops:
-        format = 'UPPER(%s%s) %s'
+        format = 'UPPER(%s) %s'
     else:
-        format = '%s%s %s'
+        format = '%s %s'
     try:
-        return format % (table_prefix, field_name,
+        return format % (field_sql,
                          backend.OPERATOR_MAPPING[lookup_type] % cast_sql)
     except KeyError:
         pass
     if lookup_type == 'in':
         in_string = ','.join(['%s' for id in value])
         if in_string:
-            return '%s%s IN (%s)' % (table_prefix, field_name, in_string)
+            return '%s IN (%s)' % (field_sql, in_string)
         else:
             raise EmptyResultSet
     elif lookup_type in ('range', 'year'):
-        return '%s%s BETWEEN %%s AND %%s' % (table_prefix, field_name)
+        return '%s BETWEEN %%s AND %%s' % field_sql
     elif lookup_type in ('month', 'day'):
-        return "%s = %%s" % backend.get_date_extract_sql(lookup_type, table_prefix + field_name)
+        return "%s = %%s" % backend.get_date_extract_sql(lookup_type, field_sql)
     elif lookup_type == 'isnull':
-        return "%s%s IS %sNULL" % (table_prefix, field_name, (not value and 'NOT ' or ''))
+        return "%s IS %sNULL" % (field_sql, (not value and 'NOT ' or ''))
     elif lookup_type == 'search':
-        return backend.get_fulltext_search_sql(table_prefix + field_name)
+        return backend.get_fulltext_search_sql(field_sql)
     elif lookup_type in ('regex', 'iregex'):
         if settings.DATABASE_ENGINE == 'oracle':
             if lookup_type == 'regex':
                 match_option = 'c'
             else:
                 match_option = 'i'
-            return "REGEXP_LIKE(%s%s, %s, '%s')" % (table_prefix, field_name, cast_sql, match_option)
+            return "REGEXP_LIKE(%s, %s, '%s')" % (field_sql, cast_sql, match_option)
         else:
             raise NotImplementedError
     raise TypeError, "Got invalid lookup_type: %s" % repr(lookup_type)
@@ -1101,7 +1106,7 @@
             # Last query term was a normal field.
             column = field.column
 
-        where.append(get_where_clause(lookup_type, current_table + '.', column, value))
+        where.append(get_where_clause(lookup_type, current_table + '.', column, value, field.db_type()))
         params.extend(field.get_db_prep_lookup(lookup_type, value))
 
     return joins, where, params
Index: django/db/backends/oracle/base.py
===================================================================
--- django/db/backends/oracle/base.py	(revision 5800)
+++ django/db/backends/oracle/base.py	(working copy)
@@ -181,6 +181,12 @@
 def get_datetime_cast_sql():
     return "TO_TIMESTAMP(%s, 'YYYY-MM-DD HH24:MI:SS.FF')"
 
+def get_field_cast_sql(db_type):
+    if db_type.endswith('LOB'):
+        return "DBMS_LOB.SUBSTR(%s%s)"
+    else:
+        return "%s%s"
+
 def get_limit_offset_sql(limit, offset=None):
     # Limits and offset are too complicated to be handled here.
     # Instead, they are handled in django/db/backends/oracle/query.py.
Index: tests/regressiontests/string_lookup/models.py
===================================================================
--- tests/regressiontests/string_lookup/models.py	(revision 5800)
+++ tests/regressiontests/string_lookup/models.py	(working copy)
@@ -36,6 +36,13 @@
     def __unicode__(self):
         return "Base %s" % self.name
 
+class Article(models.Model):
+    name = models.CharField(maxlength = 50)
+    text = models.TextField()
+
+    def __str__(self):
+        return "Article %s" % self.name
+
 __test__ = {'API_TESTS': ur"""
 # Regression test for #1661 and #1662: Check that string form referencing of
 # models works, both as pre and post reference, on all RelatedField types.
@@ -82,4 +89,13 @@
 # We can also do the above query using UTF-8 strings.
 >>> Foo.objects.get(friend__contains='\xc3\xa7')
 <Foo: Foo Bjorn>
+
+# Regression tests for #5087: make sure we can perform queries on TextFields.
+>>> a = Article(name='Test', text='The quick brown fox jumps over the lazy dog.')
+>>> a.save()
+>>> Article.objects.get(text__exact='The quick brown fox jumps over the lazy dog.')
+<Article: Article Test>
+
+>>> Article.objects.get(text__contains='quick brown fox')
+<Article: Article Test>
 """}