This document explains how to manage arrays operations on JSON documents, that stored in MapR-DB. Here you can find examples of arrays operations, which are performed using MapR-DB shell tool and OJAI Driver.
Examples use the following sample JSON document:
{
"_id": "id1",
"nested_doc_field": {
"array_field_a": [{"boolean":false}, {"decimal": 123.456}]
},
"array_field_b": ["MapR wins"]
}Note: Each of the examples depends on modified document as result of executing the previous example. Thus, if you want to try the examples it is recommended to follow them step by step.
You can use the following command to insert such document usin MapR-DB shell:
maprdb mapr:> create /sample_table
maprdb mapr:> insert /sample_table --value '{ "_id": "id1", "nested_doc_field": { "array_field_a": [{"boolean":false}, {"decimal": 123.456}] }, "array_field_b": ["MapR wins"] }'
Update operations are performed with mutations. These mutation operations are specified with sub-commands that are used to update and add document fields, or merge sub-documents to existing documents.
- Adding new element to the array
The $append sub-command allows to add one or more elements to the array. The append command is a read-modify-write type
operation that is used to append a given value to an existing binary, string or array type field.
If there is type mismatch in any intermediate field specified in fieldpath with that in the document, it fails with an
error.
MapR-DB shell example:
maprdb mapr:> jsonoptions --pretty true
maprdb mapr:> find /sample_table --id id1
maprdb mapr:> update /sample_table --id id1 --m '{ "$append":[{"nested_doc_field.array_field_a":{"some_field": "some_value"}},{"array_field_b":["First", "Second"]}] }'
maprdb mapr:> find /sample_table --id id1
You should see the new values added to the nested_doc_field.array_field_a and array_field_b arrays.
The example above is equivalent to the following code, which uses OJAI Driver:
...
// Create an OJAI connection to MapR cluster
Connection connection = DriverManager.getConnection("ojai:mapr:");
// Get an instance of OJAI DocumentStore
final DocumentStore store = connection.getStore("/sample_table");
String documentId = "id1";
// Create an instance of Map, which represents nested document. That document will be appended to the array
Map<String, String> newArrayElement = new HashMapr<>();
newArrayElement.put("some_field", "some_value");
// Create a DocumentMutation to add new array elements. Note that to append elements to the array you have to
// specify values as lists, even if there is only one element to append
DocumentMutation mutation = connection.newMutation()
.append("nested_doc_field.array_field_a", Collections.singletonList(newArrayElement))
.append("array_field_b", Arrays.asList("First", "Second"));
// Update the Document
store.update(documentId, mutation);
// Close this instance of OJAI DocumentStore
store.close();
// Close the OJAI connection and release any resources held by the connection
connection.close();
...Result:
{
"_id" : "id1",
"array_field_b" : [ "MapR wins", "First", "Second" ],
"nested_doc_field" : {
"array_field_a" : [ {
"boolean" : false
}, {
"decimal" : 123.456
}, {
"some_field" : "some_value"
} ]
}
}
- Updating an array element
The set command allows to update separate array elements. $set is a read-modify-write operation where the type of
the existing value validated at the specified FieldPath before applying the mutation. If the field does not exist in the
corresponding document in the document store, it is created. If the field exists but is not of the same type as the type
of new value, then the entire mutation fails. The list of field paths and values need to be provided as an array of
comma-separated key-value pairs. If there is a single field path, array representation is not required.
MapR-DB shell example:
maprdb mapr:> update /sample_table --id id1 --m '{ "$set":[{"nested_doc_field.array_field_a[0].boolean":true},{"array_field_b[2]":"Updated"}] }'
maprdb mapr:> find /sample_table --id id1
Note, that element of array is referenced by it's index.
The example above is equivalent to the following code, which uses OJAI Driver:
...
// Create an OJAI connection to MapR cluster
Connection connection = DriverManager.getConnection("ojai:mapr:");
// Get an instance of OJAI DocumentStore
final DocumentStore store = connection.getStore("/sample_table");
String documentId = "id1";
// Create a DocumentMutation to update the first element of 'array_field_a' array and third element of
// 'array_field_b' array
DocumentMutation mutation = connection.newMutation()
.set("nested_doc_field.array_field_a[0].boolean", true)
.set("array_field_b[2]", "Updated");
// Update the Document
store.update(documentId, mutation);
// Close this instance of OJAI DocumentStore
store.close();
// Close the OJAI connection and release any resources held by the connection
connection.close();
...Result:
{
"_id" : "id1",
"array_field_b" : [ "MapR wins", "First", "Updated" ],
"nested_doc_field" : {
"array_field_a" : [ {
"boolean" : true
}, {
"decimal" : 123.456
}, {
"some_field" : "some_value"
} ]
}
}
- Remove an element from the array
The set command allows to update separate array elements. $set is a read-modify-write operation where the type of
the existing value validated at the specified FieldPath before applying the mutation. If the field does not exist in the
corresponding document in the document store, it is created. If the field exists but is not of the same type as the type
of new value, then the entire mutation fails. The list of field paths and values need to be provided as an array of
comma-separated key-value pairs. If there is a single field path, array representation is not required.
MapR-DB shell example:
maprdb mapr:> update /sample_table --id id1 --m '{ "$delete":["nested_doc_field.array_field_a[2]","array_field_b[2]"] }'
maprdb mapr:> find /sample_table --id id1
Note, that element of array is referenced by it's index.
The example above is equivalent to the following code, which uses OJAI Driver:
...
// Create an OJAI connection to MapR cluster
Connection connection = DriverManager.getConnection("ojai:mapr:");
// Get an instance of OJAI DocumentStore
final DocumentStore store = connection.getStore("/sample_table");
String documentId = "id1";
// Create a DocumentMutation to delte the third elements of 'array_field_a' and 'array_field_b' arrays
DocumentMutation mutation = connection.newMutation()
.delete("nested_doc_field.array_field_a[2]")
.delete("array_field_b[2]");
// Update the Document
store.update(documentId, mutation);
// Close this instance of OJAI DocumentStore
store.close();
// Close the OJAI connection and release any resources held by the connection
connection.close();
...Result:
{
"_id" : "id1",
"array_field_b" : [ "MapR wins", "First" ],
"nested_doc_field" : {
"array_field_a" : [ {
"boolean" : true
}, {
"decimal" : 123.456
} ]
}
}
Finally you can drop the table from the shell using the following command:
maprdb mapr:> drop /sample_table
Next : MapR-DB Change Data Capture