feat(mssql): json is not null

- Messages TABLE
    - JsonMetaData is NOT NULL
    - json columns are checked to ensure they contain json data
- StreamMessage TYPE
    - json_metadata is NOT NULL

Author: nealmummau

src/SqlServer/src/Eventuous.SqlServer/Scripts/1_Schema.sql

@@ -26,13 +26,15 @@ IF OBJECT_ID('__schema__.Messages', 'U') IS NULL
             StreamPosition INT                   NOT NULL,
             GlobalPosition BIGINT IDENTITY (0,1) NOT NULL,
             JsonData       NVARCHAR(MAX)         NOT NULL,
-            JsonMetadata   NVARCHAR(MAX)             NULL,
+            JsonMetadata   NVARCHAR(MAX)         NOT NULL,
             Created        DATETIME2             NOT NULL,
             CONSTRAINT PK_Events PRIMARY KEY CLUSTERED (GlobalPosition),
             CONSTRAINT FK_MessageStreamId FOREIGN KEY (StreamId) REFERENCES __schema__.Streams (StreamId),
             CONSTRAINT UQ_StreamIdAndStreamPosition UNIQUE NONCLUSTERED (StreamId, StreamPosition),
             CONSTRAINT UQ_StreamIdAndMessageId UNIQUE NONCLUSTERED (StreamId, MessageId),
             CONSTRAINT CK_StreamPositionGteZero CHECK (Messages.StreamPosition >= 0),
+            CONSTRAINT CK_JsonDataIsJson CHECK (ISJSON(JsonData) = 1),
+            CONSTRAINT CK_JsonMetadataIsJson CHECK (ISJSON(JsonMetadata) = 1),
             INDEX IDX_EventsStream (StreamId)
         );
     END
@@ -54,7 +56,6 @@ IF TYPE_ID('__schema__.StreamMessage') IS NULL
             message_id    UNIQUEIDENTIFIER NOT NULL,
             message_type  NVARCHAR(128)    NOT NULL,
             json_data     NVARCHAR(MAX)    NOT NULL,
-            json_metadata NVARCHAR(MAX)        NULL
+            json_metadata NVARCHAR(MAX)    NOT NULL
         )
     END
-