关于JsonSchema转成Postgres sql ddl的小结

1. 首先，先了解下JsonSchema吧。

2. 因为最近需要快速地将json schema转成建表语句，所以以下整理总结了一个比较方便的工具类。

1) 先假设我们有一个这样的json schema文件：

{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "title": "Commodities.Forward.Forward.InstRefDataReporting.V1",
  "LastModifyDateTime": "2018-07-23T12:56:35",
  "description": "Record template for Commodities.Forward.Forward",
  "copyright": "Copyright © 2017 The Derivatives Service Bureau (BAS) Limited. All Rights Reserved.",
  "type": "object",
  "properties": {
    "TemplateVersion": {
      "title": "Template Version",
      "description": "Template Version",
      "type": "integer"
    },
    "Header": {
      "title": "Header",
      "type": "object",
      "properties": {
        "AssetClass": {
          "title": "Asset Class",
          "description": "As defined by CFI code: ISO 10962 (2015); Character #2",
          "type": "string",
          "enum": [
            "Commodities"
          ]
        },
        "InstrumentType": {
          "title": "Instrument Type",
          "description": "As defined by CFI code: ISO 10962 (2015); Character #1",
          "type": "string",
          "enum": [
            "Forward"
          ]
        }
      },
      "required": [
        "AssetClass",
        "InstrumentType"
      ],
      "additionalProperties": false
    },
    "ISIN": {
      "type": "object",
      "properties": {
        "ISIN": {
          "title": "Identification",
          "description": "International Securities Identification Number (ISO 6166)",
          "type": "string"
        },
        "Status": {
          "title": "Status",
          "description": "Status of the ISIN",
          "type": "string",
          "enum": [
            "New",
            "Updated",
            "Expired",
            "Deleted"
          ],
          "elaboration": {
            "New": "New ISIN added to the database",
            "Updated": "One/several of the fields in the ISIN record is/are updated",
            "Expired": "ISIN that has already matured relative of the specified Expiry Date",
            "Deleted": "The instrument associated with the ISIN is no longer active"
          }
        }
      },
      "required": [
        "ISIN",
        "Status"
      ],
      "additionalProperties": false
    }
  },
  "required": [
    "TemplateVersion",
    "Header",
    "ISIN"
  ],
  "additionalProperties": false
}

2) 以上，我们需要将这个文件名作为表名，properties里面的一个个object名作为字段名，特别地，object可能包含properties，这个时候就需要遍历子节点获取更深层次的字段名了。description作为字段描述，type作为字段类型。

注：这里没有约束字段长度和主键。

3. 解析json schema的工具类。

1) 读取jsonschema.json文件内容。

public static String readJsonScehma(String filePath) {
	try (InputStream in = new FileInputStream(filePath);
			BufferedReader in2 = new BufferedReader(new InputStreamReader(in))) {
		String content = "", temp = "";
		while ((temp = in2.readLine()) != null) {
			content += temp;
		}
		return content;
	} catch (IOException e) {
		e.printStackTrace();
	}
	return null;
}

2) 生成表名。

public static String generateTableName(File jsonScehmaFile) {
	String tableName = jsonScehmaFile.getName().replace(".json", "").replace(".V1", "");
	String sp[] = tableName.split("\\.");
	String markStr[] = sp[2].split("_");
	String markString = sp[2];
	if (markStr.length > 2)
		markString = markStr[markStr.length - 3] + "_" + markStr[markStr.length - 2] + "_"
				+ markStr[markStr.length - 1];
	tableName = sp[0] + "_" + sp[1] + "_" + markString;
	

	return tableName;
}

注：其实表名是自定义。而因为我的场景是有许多个诸如Commodities.Bastriver.Forward.InstRefDataReporting.json这样的schema文件，所以截取了文件名的一部分作为表名，因为postgres的表名长度不能大于63个字符。

3) 递归遍历所有properties的字段。

public static void getChildJsonObject(String nodeName, JSONObject node, JSONArray requiredObject) {
	// 遍历子节点下的所有字段和字段类型、注释
	for (Map.Entry entry : node.entrySet()) {
		// System.out.println(entry.getKey() + ":" + entry.getValue());
		JSONObject fieldsJsonObject = JSONObject.parseObject(entry.getValue().toString());
		if (fieldsJsonObject.containsKey("properties")) {
			// 有子节点
			JSONArray temp = fieldsJsonObject.getJSONArray("required");
			getChildJsonObject(entry.getKey(), fieldsJsonObject.getJSONObject("properties"), temp);
		} else {
			String description = fieldsJsonObject.getString("description");
			String type = fieldsJsonObject.getString("type");

			String fieldKey = nodeName.isEmpty() ? entry.getKey() : nodeName +"_"+ entry.getKey();
			fieldSet.add(fieldKey);
			fieldDescriptionMap.put(fieldKey, description);
			fieldTypeMap.put(fieldKey, typeMap.get(type) == null ? "Varchar(200)" : typeMap.get(type));
			fieldRequiredMap.put(fieldKey, " NULL");
			if(requiredObject != null)
				for (Object requiredName : requiredObject) {
					if (requiredName.toString().equals(entry.getKey())) {
						fieldRequiredMap.put(fieldKey, " Not NULL");
						break;
					}
				}
		}
	}
}

4. 主要是以上的遍历工具类，如果时间紧迫，也可以下载完整代码。如果有什么不懂的欢迎大家在评论区提出来。