Throw exception if multiple messages in document

Author: parkertimmins

x-pack/plugin/logsdb/src/main/java/org/elasticsearch/xpack/logsdb/patternedtext/PatternedTextFieldMapper.java

@@ -11,6 +11,7 @@
 import org.apache.lucene.document.FieldType;
 import org.apache.lucene.document.SortedSetDocValuesField;
 import org.apache.lucene.index.IndexOptions;
+import org.apache.lucene.index.IndexableField;
 import org.apache.lucene.util.BytesRef;
 import org.elasticsearch.common.util.FeatureFlag;
 import org.elasticsearch.index.IndexVersion;
@@ -132,6 +133,11 @@ protected void parseCreateField(DocumentParserContext context) throws IOExceptio
             return;
         }
 
+        var existingValue = context.doc().getField(fieldType().name());
+        if (existingValue != null) {
+            throw new IllegalArgumentException("Multiple values are not allowed for field [" + fieldType().name() + "].");
+        }
+
         // Parse template and args.
         PatternedTextValueProcessor.Parts parts = PatternedTextValueProcessor.split(value);
 

x-pack/plugin/logsdb/src/yamlRestTest/resources/rest-api-spec/test/patternedtext/10_basic.yml

@@ -308,5 +308,26 @@ tsdb:
         "dimension" : "a"
         foo: "Apache Lucene powers Elasticsearch"
 
+---
+Multiple values:
+  - do:
+      indices.create:
+        index: test1
+        body:
+          mappings:
+            properties:
+              foo:
+                type: patterned_text
+  - do:
+      catch: bad_request
+      index:
+        index: test1
+        id: "1"
+        body: {
+          "foo": [
+            "Found 5 errors for service [cheddar1]",
+            "[2020-08-18T00:58:56] Found 123 errors for service [cheddar1]"
+          ]
+        }