1#pragma once
2
3#include <Core/Block.h>
4#include <Processors/Formats/IRowInputFormat.h>
5#include <Formats/FormatSettings.h>
6#include <Common/HashTable/HashMap.h>
7
8
9namespace DB
10{
11
12class ReadBuffer;
13
14
15/** A stream for reading data in JSON format, where each row is represented by a separate JSON object.
16 * Objects can be separated by line feed, other whitespace characters in any number and possibly a comma.
17 * Fields can be listed in any order (including, in different lines there may be different order),
18 * and some fields may be missing.
19 */
20class JSONEachRowRowInputFormat : public IRowInputFormat
21{
22public:
23 JSONEachRowRowInputFormat(ReadBuffer & in_, const Block & header_, Params params_, const FormatSettings & format_settings_);
24
25 String getName() const override { return "JSONEachRowRowInputFormat"; }
26
27 bool readRow(MutableColumns & columns, RowReadExtension & ext) override;
28 bool allowSyncAfterError() const override { return true; }
29 void syncAfterError() override;
30 void resetParser() override;
31
32private:
33 const String & columnName(size_t i) const;
34 size_t columnIndex(const StringRef & name, size_t key_index);
35 bool advanceToNextKey(size_t key_index);
36 void skipUnknownField(const StringRef & name_ref);
37 StringRef readColumnName(ReadBuffer & buf);
38 void readField(size_t index, MutableColumns & columns);
39 void readJSONObject(MutableColumns & columns);
40 void readNestedData(const String & name, MutableColumns & columns);
41
42private:
43
44 const FormatSettings format_settings;
45
46 /// Buffer for the read from the stream field name. Used when you have to copy it.
47 /// Also, if processing of Nested data is in progress, it holds the common prefix
48 /// of the nested column names (so that appending the field name to it produces
49 /// the full column name)
50 String current_column_name;
51
52 /// If processing Nested data, holds the length of the common prefix
53 /// of the names of related nested columns. For example, for a table
54 /// created as follows
55 /// CREATE TABLE t (n Nested (i Int32, s String))
56 /// the nested column names are 'n.i' and 'n.s' and the nested prefix is 'n.'
57 size_t nested_prefix_length = 0;
58
59 /// Set of columns for which the values were read. The rest will be filled with default values.
60 std::vector<UInt8> read_columns;
61 /// Set of columns which already met in row. Exception is thrown if there are more than one column with the same name.
62 std::vector<UInt8> seen_columns;
63 /// These sets may be different, because if null_as_default=1 read_columns[i] will be false and seen_columns[i] will be true
64 /// for row like {..., "non-nullable column name" : null, ...}
65
66 /// Hash table match `field name -> position in the block`. NOTE You can use perfect hash map.
67 using NameMap = HashMap<StringRef, size_t, StringRefHash>;
68 NameMap name_map;
69
70 /// Cached search results for previous row (keyed as index in JSON object) - used as a hint.
71 std::vector<NameMap::LookupResult> prev_positions;
72};
73
74}
75