278 JSON Data Structures
To work with JSON data in PL/SQL, you can use these data structures.
Related Topics
278.1 JSON_ELEMENT_T Object Type
JSON_ELEMENT_T
is the supertype for the JSON_OBJECT_T
, JSON_SCALAR_T
, and JSON_ARRAY_T
object types.
Description
Note the following:
-
To create an instance of JSON_ELEMENT_T, use the
parse
function. See the “Constructors” section below for details. -
You cannot create an empty JSON_ELEMENT_T instance. To create an empty JSON container, create it based on one of the subtypes.
-
To cast a JSON_ELEMENT_T into a subtype (for example, JSON_OBJECT_T), you need to perform an explicit cast using TREAT AS. For example:
TREAT (elem AS JSON_OBJECT_T)
Constructors
You create a JSON_ELEMENT_T instance using the parse
function. The function takes as input VARCHAR2, CLOB, or BLOB data, and returns a JSON_ELEMENT_T instance.
STATIC FUNCTION parse(json VARCHAR2) RETURN JSON_ELEMENT_T STATIC FUNCTION parse(json CLOB) RETURN JSON_ELEMENT_T STATIC FUNCTION parse(json BLOB) RETURN JSON_ELEMENT_T
Only UTF8-encoded JSON is passed as a BLOB.
The parse
function takes a JSON string as input and sets up an internal representation of the JSON data. If the provided input is not valid JSON, then an error message is raised. Valid JSON has to pass the lax check of the “IS JSON” SQL condition.
Serialization
Serialization is the inverse of the parse
function. The serialization operation takes the in-memory representation of the JSON data and prints it to a string. The serialization functions and procedures are:
MEMBER FUNCTION to_String RETURN VARCHAR2 MEMBER FUNCTION to_Number RETURN NUMBER MEMBER FUNCTION to_Date RETURN DATE MEMBER FUNCTION to_Timestamp RETURN TIMESTAMP MEMBER FUNCTION to_Boolean RETURN BOOLEAN MEMBER FUNCTION to_Clob RETURN CLOB MEMBER FUNCTION to_Blob RETURN BLOB MEMBER PROCEDURE to_Clob(c IN OUT CLOB) MEMBER PROCEDURE to_Blob(c IN OUT BLOB)
The to_Clob
and to_Blob
procedures accept a CLOB or BLOB input and enable you to provide a LOB to be used as the serialization destination. For instance, EMPTY_LOB can be provided. The input LOB cannot be NULL.
If the to_Clob
function is used, then a new CLOB is created. If you do not want to create a CLOB first, then you can use the to_Clob
or to_Blob
functions, which take no parameter and generate a temp lob.
to_Blob
serializes to UTF8 format only.
Introspection
Introspection enables you to discover properties of JSON objects without modifying them. The introspection functions are:
MEMBER FUNCTION is_Object RETURN BOOLEAN MEMBER FUNCTION is_Array RETURN BOOLEAN MEMBER FUNCTION is_Scalar RETURN BOOLEAN MEMBER FUNCTION is_String RETURN BOOLEAN MEMBER FUNCTION is_Number RETURN BOOLEAN MEMBER FUNCTION is_Boolean RETURN BOOLEAN MEMBER FUNCTION is_True RETURN BOOLEAN MEMBER FUNCTION is_False RETURN BOOLEAN MEMBER FUNCTION is_Null RETURN BOOLEAN MEMBER FUNCTION is_Date RETURN BOOLEAN MEMBER FUNCTION is_Timestamp RETURN BOOLEAN MEMBER FUNCTION get_Size RETURN NUMBER
The return value of the get_size
function depends on the JSON type:
-
For a scalar, it returns
1
. -
For an object, it returns the number of keys.
-
For an array, it returns the number of items.
Note that JSON does not support dates and timestamps natively. Instead they are typically modeled as strings. The DOM API enables you to add dates and timestamps as scalar values and preserve them until serialization to JSON, where they are printed as string following the ISO 8601 format. If a SQL value of type date or timestamp has been added, then the is_Date
and is_Timestamp
functions return true. If a date has been added as a string (e.g. as ISO 8601), then the is_Date
and is_Timestamp
functions return false. You can use Oracle conversion function to_Date
and to_Timestamp
to convert a string representation of a date, and timestamp to the Oracle representation.
Error Handling
You can set the level of error handling for JSON processing. You might not want an error to be raised for every mismatch. The on_Error
procedure enables you to specify when errors should be raised:
MEMBER PROCEDURE on_Error(value NUMBER)
The on_Error
procedure defines what happens if an error is encountered during a PL/SQL operation, for instance, a get call.
The default is to not raise an error but to return NULL instead.
You invoke On_error
on a JSON_ELEMENT_T instance and it sets the error behavior for all subsequent calls. To reset the behavior to the default, you can call on_Error(0)
.
Values for the value
parameter are:
Table 278-1 Values for the value Parameter in the ON_ERROR Procedure
Value | Description |
---|---|
0 | Reset to the default behavior, which is to return NULL instead of raising an error. |
1 | Raise all errors. |
2 | Raise an error if no value is detected. |
3 | Raise an error if the data types do not match, for example, if you call GET_NUMBER on a string value. |
4 | Raise an error if the input is invalid, for example, if the array is out of bounds. |
You can combine values. For example, you can specify 7 to indicate a combination of 3 and 4.
In the following example, an error is raised because the value of “a” is “xyz”, which cannot be converted to a number. If the on_Error
procedure had not been called, then NULL would be returned, and no error would be raised.
declare jo JSON_OBJECT_T; begin jo := JSON_OBJECT_T.parse('{a:"xyz"}'); jo.On_error(1); dbms_output.put_line(jo.get_Number('a')); end; /
278.2 JSON_OBJECT_T Object Type
JSON_OBJECT_T
is a subtype of the JSON_ELEMENT_T object type. It corresponds to the JSON object structure.
Constructors
You can create an empty JSON_OBJECT_T instance using the following constructor.
CONSTRUCTOR FUNCTION JSON_OBJECT_T RETURN SELF AS RESULT
You can create a JSON_OBJECT_T instance using one of the following parse
functions:
STATIC FUNCTION parse(json VARCHAR2) RETURN JSON_OBJECT_T STATIC FUNCTION parse(json CLOB) RETURN JSON_OBJECT_T STATIC FUNCTION parse(json BLOB) RETURN JSON_OBJECT_T
You can also create a JSON_OBJECT_T instance using one of the following constructors:
CONSTRUCTOR FUNCTION JSON_OBJECT_T(jsn VARCHAR2) RETURN SELF AS RESULT, CONSTRUCTOR FUNCTION JSON_OBJECT_T(jsn CLOB) RETURN SELF AS RESULT, CONSTRUCTOR FUNCTION JSON_OBJECT_T(jsn BLOB) RETURN SELF AS RESULT, CONSTRUCTOR FUNCTION JSON_OBJECT_T(e JSON_ELEMENT_T) RETURN SELF AS RESULT
Only UTF8-encoded JSON is passed as a BLOB.
The parse
function takes a JSON string as input and sets up an internal representation of the JSON data. If the provided input is not a valid JSON object, then an error message is raised. The input has to specify a JSON object, not an array.
Get Functions and Procedures
The following functions and procedures enable you to retrieve the value of the JSON object:
MEMBER FUNCTION get(key VARCHAR2) RETURN JSON_ELEMENT_T MEMBER FUNCTION get_String(key VARCHAR2) RETURN VARCHAR2 MEMBER FUNCTION get_Number(key VARCHAR2) RETURN NUMBER MEMBER FUNCTION get_Date(key VARCHAR2) RETURN DATE MEMBER FUNCTION get_Timestamp(key VARCHAR2) RETURN TIMESTAMP MEMBER FUNCTION get_Boolean(key VARCHAR2) RETURN BOOLEAN MEMBER FUNCTION get_Clob(key VARCHAR2) RETURN CLOB MEMBER FUNCTION get_Blob(key VARCHAR2) RETURN BLOB MEMBER FUNCTION get_Object(key VARCHAR2) RETURN JSON_OBJECT_T MEMBER FUNCTION get_Array(key VARCHAR2) RETURN JSON_ARRAY_T MEMBER PROCEDURE get_Clob(key NUMBER, c IN OUT CLOB) MEMBER PROCEDURE get_Blob(key NUMBER, c IN OUT BLOB)
Note:
-
The
get
function has reference semantics. This means that if the returned JSON_ELEMENT_T is modified, then the containing JSON_ELEMENT_T is also changed. See the Reference Semantics section below for details. -
The
GET_STRING
function converts the value to a string if it is not already a string. Thus, theGET_STRING
function returns a non-null value even if IS_STRING returns false. -
All the “get” functions perform a conversion if possible. If no conversion is possible, then an error might be raised, depending on what
ON_ERROR
is set to.
The GET_CLOB
and GET_BLOB
procedures, which accept a CLOB or BLOB as input, enable you to provide a LOB to be used as serialization destination. For instance, EMPTY_LOB can be provided. If you use the GET_CLOB
function instead, then a new CLOB will be created implicitly. The input LOB cannot be NULL. If you do not want to create a BLOB or CLOB first, you can use the GET_CLOB or GET_BLOB functions, which take no parameter and generates a temp LOB.
GET_BLOB
serializes to UTF8 format only.
Set Procedures
The following procedures enable you to set the value of a JSON object. Existing values, if present, will be overwritten.
MEMBER PROCEDURE put(key VARCHAR2, value JSON_ELEMENT_T) MEMBER PROCEDURE put(key VARCHAR2, value VARCHAR2) MEMBER PROCEDURE put(key VARCHAR2, value NUMBER) MEMBER PROCEDURE put(key VARCHAR2, value BOOLEAN) MEMBER PROCEDURE put(key VARCHAR2, value DATE) MEMBER PROCEDURE put(key VARCHAR2, value TIMESTAMP) MEMBER PROCEDURE put_Null(key VARCHAR2)
Introspection Functions
Introspection enables you to discover properties of JSON objects without modifying them. The introspection functions are:
MEMBER FUNCTION has(key VARCHAR2) RETURN BOOLEAN MEMBER FUNCTION get_Type(key VARCHAR2) RETURN VARCHAR2 MEMBER FUNCTION get_Keys RETURN JSON_KEY_LIST
The get_Keys function returns an object type of JSON_KEY_LIST, which is a varray of VARCHAR2(4000). The varray contains the names of keys in the JSON object. The get_Keys function returns at most 32767 field names for a given JSON object. An error is raised if it is applied to an object with more than 32767 fields.
The example below walks through the items of the varray to build a JSON_ARRAY_T object that contains all key names.
declare jo JSON_OBJECT_T; ja JSON_ARRAY_T; keys JSON_KEY_LIST; keys_string VARCHAR2(100); begin ja := new JSON_ARRAY_T; jo := JSON_OBJECT_T.parse('{"name":"fred", "jobTitle":"codemonkey", "projects":["json", "xml"]}'); keys := jo.get_keys; for i in 1..keys.count loop ja.append(keys(i)); end loop; keys_string := ja.to_string; dbms_output.put_line(keys_string); end; /
The output is:
["name","jobTitle","projects"]
Modification Procedures
The following procedures enable you to remove or rename keys in a JSON object.
MEMBER PROCEDURE remove(key VARCHAR2) MEMBER PROCEDURE rename_Key(keyOld VARCHAR2, keyNew VARCHAR2)
Duplicate key names are not supported and will raise an error.
Clone Function
This function makes a copy of the JSON object. Reference semantics is changed to value semantics.
MEMBER FUNCTION clone RETURN JSON_OBJECT_T
Reference Semantics
Calling the get
function that returns a JSON_ELEMENT_T object always returns a reference to the complex values instead of a copy. This means that changing the returned value affects its container. See the example below.
declare data JSON_OBJECT_T; address JSON_OBJECT_T; zip number; begin data := new JSON_OBJECT_T('{ "first": "John", "last": "Doe", "address": { "country": "USA", "zip": "94065" } }'); address := data.get_object('address'); dbms_output.put_line(address.to_string); -- 1) VALUE SEMANTICS for scalar values -- (changing the value has no effect on container) zip := address.get_number('zip'); dbms_output.put_line(zip); zip := 12345; dbms_output.put_line(zip); -- address is still the same dbms_output.put_line(address.to_string); -- 2) REFERENCE SEMANTICS for complex values -- 'address' is a reference to the complex address values inside 'data' address.put('zip', 12345); address.put('street', 'Detour Road'); dbms_output.put_line(data.to_string); end; /
In cases where you do not want the reference semantics, you can use the clone
function to create a copy of the returned object. This decouples the value from its container. In the example above, you can create a copy of the “address” object by replacing this line:
address := data.get_object('address');
with this line:
address := data.get_object('address').clone;
After this, changing the address with have no effect on the value of the ‘data’ containing object.
Update Example
The following example updates the price of an item by 10%.
WITH FUNCTION updatePrice(jsonTxt in VARCHAR2 ) RETURN VARCHAR2 IS jo JSON_OBJECT_T; oldPrice NUMBER; BEGIN jo := new JSON_OBJECT_T(jsonTxt); oldPrice := jo.get_number('price'); jo.put('price', oldPrice * 1.1); RETURN jo.to_string(); END; SELECT updatePrice(col) FROM t1;
278.3 JSON_ARRAY_T Object Type
JSON_ARRAY_T
is a subtype of the JSON_ELEMENT_T
object type. JSON_ARRAY_T
corresponds to the JSON array structure.
Constructors
You can create an empty JSON_ARRAY_T instance using the following constructor.
CONSTRUCTOR FUNCTION JSON_ARRAY_T RETURN SELF AS RESULT
You can create a JSON_ARRAY_T instance using one the following parse
functions:
STATIC FUNCTION parse(json VARCHAR2) RETURN JSON_ARRAY_T STATIC FUNCTION parse(json CLOB) RETURN JSON_ARRAY_T STATIC FUNCTION parse(json BLOB) RETURN JSON_ARRAY_T
You can also create a JSON_ARRAY_T instance using one the following constructors:
CONSTRUCTOR FUNCTION JSON_Array_T(jsn VARCHAR2) RETURN SELF AS RESULT CONSTRUCTOR FUNCTION JSON_Array_T(jsn CLOB) RETURN SELF AS RESULT CONSTRUCTOR FUNCTION JSON_Array_T(jsn BLOB) RETURN SELF AS RESULT CONSTRUCTOR FUNCTION JSON_Array_T(e JSON_ELEMENT_T) RETURN SELF AS RESULT
Only UTF8-encoded JSON is passed as a BLOB.
The parse
function takes a JSON string as input and sets up an internal representation of the JSON data. If the provided input is not valid JSON, then an error message is raised. The input has to specify a JSON array, not an object.
Get Functions and Procedures
The following functions and procedures enable you to retrieve the value of the JSON array:
MEMBER FUNCTION get(pos NUMBER) RETURN JSON_ELEMENT_T MEMBER FUNCTION get_String(pos NUMBER) RETURN VARCHAR2 MEMBER FUNCTION get_Number(pos NUMBER) RETURN NUMBER MEMBER FUNCTION get_Date(pos NUMBER) RETURN DATE MEMBER FUNCTION get_Timestamp(pos NUMBER) RETURN TIMESTAMP MEMBER FUNCTION get_Boolean(pos NUMBER) RETURN BOOLEAN MEMBER FUNCTION get_Clob(pos NUMBER) RETURN CLOB MEMBER FUNCTION get_Blob(pos NUMBER) RETURN BLOB MEMBER PROCEDURE get_Clob(pos NUMBER, c IN OUT CLOB) MEMBER PROCEDURE get_Blob(pos NUMBER, c IN OUT BLOB)
Note:
-
The
get
function has reference semantics. This means that if the returned JSON_ELEMENT_T is modified, then the containing JSON_ELEMENT_T is changed too. -
The
GET_STRING
function converts the value to a string if it is not already a string. The function returns a non-null value even if IS_STRING returns false. -
All the “get” functions perform a conversion if possible. If no conversion is possible, then an error might be raised, depending on what
ON_ERROR
is set to.
The GET_CLOB
and GET_BLOB
procedures, which accept a CLOB or BLOB as input, enable you to provide a LOB to be used as serialization destination. For instance, EMPTY_LOB can be provided. If you use the GET_CLOB
function instead, then a new CLOB will be created implicitly. The input LOB cannot be NULL. If you do not want to create a BLOB or CLOB first, you can use the GET_CLOB or GET_BLOB functions, which take no parameter and generates a temp LOB.
GET_BLOB
serializes to UTF8 format only.
Set Procedures
The following procedures enable you to set the value at the specified position in the JSON array. These procedures insert (not overwrite) at the specified position unless overwrite is requested.
MEMBER PROCEDURE put(pos NUMBER, value VARCHAR2, overwrite BOOLEAN DEFAULT FALSE) MEMBER PROCEDURE put(pos NUMBER, value NUMBER, overwrite BOOLEAN DEFAULT FALSE) MEMBER PROCEDURE put(pos NUMBER, value BOOLEAN, overwrite BOOLEAN DEFAULT FALSE) MEMBER PROCEDURE put(pos NUMBER, value JSON_ELEMENT_T, overwrite BOOLEAN DEFAULT FALSE) MEMBER PROCEDURE put(pos NUMBER, value DATE, overwrite BOOLEAN DEFAULT FALSE) MEMBER PROCEDURE put(pos NUMBER, value TIMESTAMP, overwrite BOOLEAN DEFAULT FALSE) MEMBER PROCEDURE put_Null(pos NUMBER, overwrite BOOLEAN DEFAULT FALSE)
The following procedures append the specified value to the end of the JSON array:
MEMBER PROCEDURE append(value JSON_ELEMENT_T) MEMBER PROCEDURE append(value VARCHAR2) MEMBER PROCEDURE append(value NUMBER) MEMBER PROCEDURE append(value BOOLEAN) MEMBER PROCEDURE append(value DATE) MEMBER PROCEDURE append(value TIMESTAMP) MEMBER PROCEDURE append_Null
Introspection Function
Introspection enables you to discover properties of the JSON array without modifying them.
MEMBER FUNCTION get_Type(pos NUMBER) RETURN VARCHAR2
Modification Procedure
The following procedure enables you to remove the value at the specified position in the JSON array.
MEMBER PROCEDURE remove(pos NUMBER)
Clone Function
This function makes a copy of the JSON array. Reference semantics is changed to value semantics.
MEMBER FUNCTION clone RETURN JSON_ARRAY_T
278.4 JSON_SCALAR_T Object Type
JSON_SCALAR_T
is a subtype of the JSON_ELEMENT_T
object type.
Description
A JSON_SCALAR_T
instance captures one scalar values, for example, the string “fred” or the number 1. This type does not have any functions or procedures other than the ones inherited from JSON_ELEMENT_T.
You cannot create an instance of this type directly.
278.5 JSON_KEY_LIST Type
JSON_KEY_LIST
is a varray of VARCHAR2(4000)
.
Description
This type is used by the get_Keys
function in the JSON_OBJECT_T Object Type.